Semiconductor device

ABSTRACT

Provided is a semiconductor device in which on-resistance is largely reduced. In a region ( 2   a ) of an N type epitaxial layer ( 2 ) of the semiconductor device  20 , each region between neighboring trenches ( 3 ) is blocked with a depletion layer ( 14 ) formed around a trench ( 3 ) so that a current passage ( 12 ) is interrupted, while a part of the depletion layer ( 14 ) formed around the trench ( 3 ) is deleted so that the current passage ( 12 ) is opened. In a region ( 2   b ), a junction portion ( 8 ) between the N type epitaxial layer ( 2 ) and a P +  type diffusion region ( 7 ) makes a Zener diode ( 8 ).

TECHNICAL FIELD

The present invention relates to a semiconductor device, and moreparticularly, to a semiconductor device having a switching function orthe like.

BACKGROUND ART

Conventionally, a metal oxide semiconductor field effect transistor(MOSFET) is known as a semiconductor device having a switching function(see, for example, Patent Document 1). The Patent Document 1 discloses atrench gate MOSFET (semiconductor device) in which a gate electrode isembedded in a trench formed in a semiconductor layer.

FIG. 46 is a cross sectional view illustrating a structure of aconventional MOSFET (semiconductor device) disclosed in the PatentDocument 1. With reference to FIG. 46, the conventional MOSFET(semiconductor device) includes an N⁺ type semiconductor substrate 301and an epitaxial layer (semiconductor layer) 302 formed on the uppersurface of the semiconductor substrate 301. This epitaxial layer 302includes an N⁻ type impurity region (drain region) 302 a, a P typeimpurity region 302 b and an N⁺ type impurity region (source region) 302c formed in this order from the semiconductor substrate 301 side.

In addition, the epitaxial layer 302 is provided with a trench 303 thatis formed so as to penetrate the N⁺ type impurity region 302 c and the Ptype impurity region 302 b and to reach a halfway depth of the N⁻ typeimpurity region 302 a. A gate electrode 305 is embedded in the trench303 via a gate insulator film 304. In addition, an interlayer insulatorfilm 306 is formed on the upper surface of the epitaxial layer 302 so asto close the opening end of the trench 303.

In addition, a source electrode 307 is formed on the upper surface ofthe epitaxial layer 302 so as to cover the interlayer insulator film306. In addition, a drain electrode 308 is formed on the back surface ofthe semiconductor substrate 301.

In the conventional MOSFET having the above-mentioned structure, appliedvoltage to the gate electrode 305 is changed for on-off control.

Specifically, when a predetermined positive potential is applied to thegate electrode 305, minority carrier (electrons) in the P type impurityregion 302 b is attracted to the trench 303 side, and an inversion layer309 is formed, which connects the N⁻ type impurity region (drain region)302 a with the N⁺ type impurity region (source region) 302 c. Thus,current can flow between the source electrode 307 and the drainelectrode 308 via the inversion layer 309. As a result, the MOSFET isturned on.

In this way, in the conventional MOSFET, the inversion layer 309, whichis formed so as to connect the N⁻ type impurity region (drain region)302 a with the N⁺ type impurity region (source region) 302 c, is made tofunction as a channel.

In addition, when the application of the predetermined positivepotential to the gate electrode 305 is stopped from the above-mentionedstate, the inversion layer (channel) 309 disappears so that the currentflowing between the source electrode 307 and the drain electrode 308 canbe interrupted. As a result, the MOSFET is turned off.

Patent Document 1: JP-A-2001-7149

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

However, in the conventional structure illustrated in FIG. 46, theinversion layer (channel) 309 formed in the turned-on state is verythin, so there is a disadvantage that it is difficult to reduceresistance against the current flowing in the inversion layer (channel)309. As a result, there is a problem that it is difficult to improveon-resistance.

The present invention is created to solve the above-mentioned problem,and it is an object of the present invention to provide a semiconductordevice that can largely reduce on-resistance based on a new principle ofoperation.

Means for Solving the Problem

In order to achieve the above-mentioned purpose, a semiconductor deviceaccording to a first aspect of the present invention includes asemiconductor layer of one conductivity type including an inside regionand an outside region disposed outside the inside region, a plurality oftrenches formed in the inside region of the semiconductor layer so as tobe arranged with predetermined spaces, an opening end of each of thetrenches being positioned on an upper surface side of the semiconductorlayer, a plurality of diffusion regions of an inverse conductivity typeformed in the outside region of the semiconductor layer so as to bearranged with predetermined spaces, an upper surface of each of thediffusion regions being exposed to the upper surface side of thesemiconductor layer, a plurality of embedded electrodes filled in theplurality of trenches, and an electrode layer formed on the uppersurface of the semiconductor layer so as to cover the inside region andthe outside region of the semiconductor layer. Further, the insideregion of the semiconductor layer has a structure in which each regionbetween the neighboring trenches in the semiconductor layer becomes acurrent passage, and each region between the neighboring trenches in thesemiconductor layer is blocked with a depletion layer formed around thetrench so that the current passage is interrupted, while at least a partof the depletion layer formed around the trench is deleted so that thecurrent passage is opened. A junction portion between the semiconductorlayer and the diffusion region makes a Zener diode in the outside regionof the semiconductor layer.

In the semiconductor device according to the first aspect, as describedabove, the plurality of trenches filled with the embedded electrode areformed in the inside region of the semiconductor layer of oneconductivity type. Each region between the neighboring trenches in thesemiconductor layer is blocked with the depletion layer formed aroundthe trench so that the current passage (each region between theneighboring trenches in the semiconductor layer) is interrupted, whileat least a part of the depletion layer formed around the trench isdeleted so that the current passage (each region between the neighboringtrenches in the semiconductor layer) is opened. For instance, if theembedded electrode is formed on the inner surface of the trench via aninsulator film, a formation state of the depletion layer formed aroundthe trench changes in accordance with applied voltage to the embeddedelectrode. Therefore, by controlling the applied voltage to the embeddedelectrode, it is possible to switch from the turned-on state (in whichthe current passage is opened) to the turned-off state (in which thecurrent passage is interrupted), and to switch in the oppositedirection. In other words, the semiconductor device can be used as aswitch device (switching transistor). Further, in the above-mentionedstructure, in the turned-on state, current can flow through the entirepart of the current passage (each region between the neighboringtrenches in the semiconductor layer) in which the depletion layer isdeleted. Therefore, compared with the conventional MOSFET (semiconductordevice) in which a very thin inversion layer functions as the channel(current passage), resistance against current can be reduced largely.Thus, compared with the conventional MOSFET (semiconductor device) inwhich a very thin inversion layer functions as the channel (currentpassage), on-resistance can be reduced largely.

In addition, in the semiconductor device according to the first aspect,as described above, a plurality of diffusion regions of an inverseconductivity type is formed in the outside region disposed outside theinside region in the semiconductor layer of one conductivity type, andthe junction portion between the semiconductor layer and the diffusionregion makes a Zener diode. Thus, it is possible to connect the Zenerdiode between the source and the drain of the switching transistor.Thus, even if noise voltage, surge voltage or the like enters thesemiconductor device, the noise voltage, the surge voltage or the likecan be absorbed by the Zener diode. Thus, it is possible to suppressmalfunction such as breakage of the semiconductor device due to thenoise voltage, the surge voltage or the like entering the semiconductordevice.

In addition, in the above-mentioned structure, the switching transistorand the Zener diode are integrated, so it is not necessary to disposeanother region or the like for forming a wiring member for connectingthe switching transistor with the Zener diode. Thus, an area of thecircuit including the switching transistor and the Zener diode that areconnected to each other can be reduced.

In the semiconductor device according to the first aspect, preferably, ajunction portion between each region between the neighboring diffusionregions of the semiconductor layer and the electrode layer makes aSchottky barrier diode in the outside region of the semiconductor layer.With this structure, between the source and the drain of the switchingtransistor, the Schottky barrier diode having shorter reverse recoverytime than the Zener diode can further be connected in addition to theZener diode. Thus, a decrease of the switching speed can be suppressed.

In addition, in the above-mentioned structure, the switching transistor,the Zener diode and the Schottky barrier diode are integrated.Therefore, it is not necessary to dispose another region or the like forforming a wiring member for connecting the switching transistor, theZener diode and the Schottky barrier diode with each other. Thus, anarea of the circuit including the switching transistor, the Zener diodeand the Schottky barrier diode that are connected to each other can bereduced.

In this case, preferably, when a reverse bias is applied to the junctionportion between each region between the neighboring diffusion regions ofthe semiconductor layer and the electrode layer in the outside region ofthe semiconductor layer, each region between the neighboring diffusionregions of the semiconductor layer is blocked with a depletion layerformed around the diffusion region. With this structure, when thereverse bias is applied to the Schottky barrier diode, current flowingthrough each region between the neighboring diffusion regions in thesemiconductor layer can be interrupted. Thus, occurrence of leak currentin the Schottky barrier diode can be suppressed.

Further, in the above-mentioned case, preferably, when the reverse biasis applied to the junction portion between each region between theneighboring diffusion regions of the semiconductor layer and theelectrode layer in the outside region of the semiconductor layer, thedepletion layers formed around the neighboring diffusion regions areconnected to each other. With this structure, each region between theneighboring diffusion regions in the semiconductor layer can securely beblocked with the depletion layers.

Further, in the above-mentioned case, preferably, in the outside regionof the semiconductor layer, a distance between the neighboring diffusionregions is set so that the depletion layers formed around theneighboring diffusion regions are overlapped with each other. With thisstructure, the depletion layers formed around the neighboring diffusionregions can easily be connected to each other.

In the semiconductor device according to the first aspect, it ispossible to adopt the structure in which each region between theneighboring trenches is blocked with every depletion layer formed aroundeach of the plurality of trenches so that the current passage isinterrupted, while every depletion layer formed around each of theplurality of trenches is deleted so that the current passage is opened.

In the semiconductor device according to the first aspect, it ispossible to adopt the structure in which the plurality of embeddedelectrodes include two types that are first embedded electrodes andsecond embedded electrodes to which voltages are applied separately, andeach region between the neighboring trenches is blocked with thedepletion layer formed around every trench among the plurality oftrenches so that the current passage is interrupted, while the depletionlayer formed around the trench filled with the first embedded electrodeamong the plurality of trenches is deleted so that the current passageis opened.

In this case, the second embedded electrode may have a Schottky contactwith the semiconductor layer inside the trench.

The semiconductor device according to the first aspect may furtherinclude a current passage interrupting diffusion region of an inverseconductivity type formed in each region between the neighboring trenchesof the semiconductor layer so as to be disposed with a predeterminedspace to the trench, in which each region between the neighboringtrenches is blocked with depletion layers formed around the trench andaround the current passage interrupting diffusion region so that thecurrent passage is interrupted, while the depletion layer formed aroundthe trench is deleted so that the current passage is opened.

Further, the semiconductor device according to the first aspect may havethe structure in which when the current passage is interrupted, thedepletion layers formed around the neighboring trenches are connected toeach other. With this structure, each region between the neighboringtrenches in the semiconductor layer can securely be blocked with thedepletion layers.

Further, in the semiconductor device according to the first aspect, adistance between the neighboring trenches may be set so that thedepletion layers formed around the neighboring trenches are overlappedwith each other. With this structure, the depletion layers formed aroundthe neighboring trenches can easily be connected to each other.

In addition, the semiconductor device according to the first aspect mayfurther include an interlayer insulator film for insulating between theembedded electrode and the electrode layer, in which the embeddedelectrode is filled in the trench to a halfway depth, and the interlayerinsulator film is filled in the remaining part of the trench that is notfilled with the embedded electrode so that the upper surface of theinterlayer insulator film becomes flush with the upper surface of thesemiconductor layer. With this structure, even if a distance between theneighboring trenches is made to be small, the part of the upper surfaceside of the semiconductor layer (upper end portion of the region betweenthe neighboring trenches in the semiconductor layer) is not entirelycovered with the interlayer insulator film. Thus, the distance betweenthe neighboring trenches can be reduced, so that the depletion layersformed around the neighboring trenches can easily be connected to eachother.

A semiconductor device according to a second aspect of the presentinvention includes a semiconductor layer including first region of oneconductivity type, and a second region of one conductivity type as wellas a third region of an inverse conductivity type formed on the firstregion, a plurality of trenches formed in at least the second region ofthe semiconductor layer so as to be arranged with predetermined spaces,an opening end of each of the trenches being positioned on an uppersurface side of the semiconductor layer, and a plurality of embeddedelectrodes filled in the plurality of trenches. Further, each regionbetween the neighboring trenches in the second region becomes a currentpassage, and each region between the neighboring trenches in the secondregion is blocked with a depletion layer formed around the trench sothat the current passage is interrupted, while the at least a part ofthe depletion layer formed around the trench is deleted so that thecurrent passage is opened. A bidirectional Zener diode constituted ofthe plurality of diffusion regions is formed in the third region of thesemiconductor layer. Note that the semiconductor layer of the presentinvention includes the semiconductor substrate.

In the semiconductor device according to the second aspect, as describedabove, at least in the second region of the semiconductor layer of oneconductivity type, a plurality of trenches filled with the embeddedelectrode are formed, and each region between the neighboring trenchesin the semiconductor layer is blocked with the depletion layer formedaround the trench so that the current passage (each region between theneighboring trenches in the semiconductor layer) is interrupted, whileat least a part of the depletion layer formed around the trench isdeleted so that the current passage (each region between the neighboringtrenches in the semiconductor layer) is opened. Thus, if the embeddedelectrode is formed on the inner surface of the trench via the insulatorfilm for example, a formation state of the depletion layer formed aroundthe trench changes in accordance with the applied voltage to theembedded electrode. Therefore, by controlling the applied voltage to theembedded electrode, it is possible to switch from the turned-on state(in which the current passage is opened) to the turned-off state (inwhich the current passage is interrupted), and to switch in the oppositedirection. In other words, the semiconductor device can be used as aswitch device (switching transistor). Further, in the above-mentionedstructure, in the turned-on state, current can flow through the entirepart of the current passage (each region between the neighboringtrenches in the semiconductor layer) in which the depletion layer isdeleted. Therefore, compared with the conventional MOSFET (semiconductordevice) in which a very thin inversion layer functions as the channel(current passage), on-resistance can be reduced largely.

In addition, in the semiconductor device according to the second aspect,as described above, the bidirectional Zener diode made of a plurality ofdiffusion regions is formed in the third region so that thebidirectional Zener diode can be connected between the source and thedrain as well as between the source and the gate of the switchingtransistor. Thus, even if static electricity, surge voltage or the likeenters the semiconductor device, the static electricity, the surgevoltage or the like can be absorbed by the bidirectional Zener diode.Therefore, it is possible to suppress dielectric breakdown or the likedue to the static electricity, the surge voltage or the like enteringthe semiconductor device. As a result, it is possible to suppressoccurrence of a malfunction such as a breakage of the semiconductordevice due to dielectric breakdown or the like.

In addition, in the above-mentioned structure, the switching transistorand the bidirectional Zener diode are integrated, so it is not necessaryto dispose another region or the like for forming a wiring member forconnecting the switching transistor with the bidirectional Zener diode.Thus, an area of the circuit including the switching transistor and thebidirectional Zener diode that are connected to each other can bereduced.

The semiconductor device according to the second aspect may furtherinclude an electrode layer formed on at least the second region of thesemiconductor layer, so that the second region of the semiconductorlayer and a first part of the plurality of diffusion regionsconstituting the bidirectional Zener diode can be electrically connectedvia the electrode layer.

In this case, preferably, there is further provided a fourth region ofone conductivity type formed on the first region, and a second part ofthe plurality of diffusion regions constituting the bidirectional Zenerdiode is electrically connected to the first region via the fourthregion. With this structure, the bidirectional Zener diode can easily beconnected between the source and the drain of the switching transistor.

In the above-mentioned structure including the electrode layer,preferably, a third part of the plurality of diffusion regionsconstituting the bidirectional Zener diode is electrically connected apredetermined embedded electrode among the plurality of embeddedelectrodes. With this structure, the bidirectional Zener diode caneasily be connected between the gate and the source of the switchingtransistor.

In the semiconductor device according to the second aspect, preferably,the plurality of diffusion regions constituting the bidirectional Zenerdiode include first diffusion regions of one conductivity type andsecond diffusion regions of an inverse conductivity type. The firstdiffusion regions are arranged with predetermined spaces, and the seconddiffusion region is arranged between the neighboring first diffusionregions so as to contact with the first diffusion regions in a planview. With this structure, the bidirectional Zener diode can easily beformed in the third region.

In addition, in the above-mentioned structure, by changing the number ofthe formed first diffusion regions and second diffusion regions, Zenervoltage (breakdown voltage) of the bidirectional Zener diode can easilybe adjusted. Therefore, the bidirectional Zener diode having apredetermined Zener voltage (breakdown voltage) can easily be connectedbetween the source and the drain of the switching transistor as well asbetween the source and the gate of the same.

In the above-mentioned structure including the fourth region, the thirdregion may be formed in a region outside the second region so as toenclose the second region in a plan view, and the fourth region may beformed in a region outside the third region so as to enclose the thirdregion in a plan view.

The semiconductor device according to the second aspect may have thestructure in which each region between the neighboring trenches isblocked with every depletion layer formed around each of the pluralityof trenches so that the current passage is interrupted, while everydepletion layer formed around each of the plurality of trenches isdeleted so that the current passage is opened.

The semiconductor device according to the second aspect may have thestructure in which the plurality of embedded electrodes include twotypes that are first embedded electrodes and second embedded electrodesto which voltages are applied separately, and each region between theneighboring trenches is blocked with the depletion layer formed aroundevery trench among the plurality of trenches so that the current passageis interrupted, while the depletion layer formed around the trenchfilled with the first embedded electrode among the plurality of trenchesis deleted so that the current passage is opened.

In this case, the second embedded electrode may have a Schottky contactwith the semiconductor layer inside the trench.

The semiconductor device according to the second aspect may furtherinclude a current passage interrupting diffusion region of an inverseconductivity type formed in each region between the neighboring trenchesof the semiconductor layer so as to be disposed with a predeterminedspace to the trench, in which each region between the neighboringtrenches is blocked with depletion layers formed around the trench andaround the current passage interrupting diffusion region so that thecurrent passage is interrupted, while the depletion layer formed aroundthe trench is deleted so that the current passage is opened.

Note that in the semiconductor device according to the second aspect,when current flowing through each region between the neighboringtrenches in the second region is to be interrupted, the depletion layersformed around the neighboring trenches may be connected to each other.With this structure, each region between the neighboring trenches in thesemiconductor layer can securely be blocked with the depletion layersformed around the neighboring trenches.

In addition, the semiconductor device according to the second aspect mayfurther include an interlayer insulator film formed on the upper surfaceof the embedded electrode, in which the embedded electrode is filled inthe trench to a halfway depth, and the interlayer insulator film isfilled in the remaining part of the trench that is not filled with theembedded electrode so that the upper surface of the interlayer insulatorfilm becomes flush with the upper surface of the semiconductor layer.With this structure, even if a distance between the neighboring trenchesis made to be small, the part of the upper surface side of thesemiconductor layer (upper end portion of the region between theneighboring trenches in the semiconductor layer) is not entirely coveredwith the interlayer insulator film. Thus, the distance between theneighboring trenches can be reduced, so that the depletion layers formedaround the neighboring trenches can easily be connected to each other.

A semiconductor device according to a third aspect of the presentinvention includes a semiconductor layer including first region of oneconductivity type, a second region of one conductivity type formed onthe first region and a third region of an inverse conductivity type, aplurality of trenches formed in at least the second region of thesemiconductor layer so as to be arranged with predetermined spaces, anda plurality of embedded electrodes filled in the plurality of trenches.Further, each region between the neighboring trenches in thesemiconductor layer becomes a current passage, and each region betweenthe neighboring trenches is blocked with a depletion layer formed aroundthe trench so that the current passage is interrupted, while at least apart of the depletion layer formed around the trench is deleted so thatthe current passage is opened. A junction portion between the firstregion and the third region makes a Zener diode.

In the semiconductor device according to the third aspect, as describedabove, a plurality of trenches filled with the embedded electrode areformed in the second region of one conductivity type that is formed onthe first region of one conductivity type, and each region between theneighboring trenches is blocked with the depletion layer formed aroundthe trench so that the current passage (each region between theneighboring trenches in the semiconductor layer) is interrupted, whileat least a part of the depletion layer formed around the trench isdeleted so that the current passage (each region between the neighboringtrenches in the semiconductor layer) is opened. Thus, if the embeddedelectrode is formed on the inner surface of the trench via the insulatorfilm for example, a formation state of the depletion layer formed aroundthe trench changes in accordance with the applied voltage to theembedded electrode. Therefore, by controlling the applied voltage to theembedded electrode, it is possible to switch from the turned-on state(in which the current passage is opened) to the turned-off state (inwhich the current passage is interrupted), and to switch in the oppositedirection. In other words, the semiconductor device can be used as aswitch device (switching transistor). Further, in the above-mentionedstructure, in the turned-on state, current can flow through the entirepart of the current passage (each region between the neighboringtrenches in the semiconductor layer) in which the depletion layer isdeleted. Therefore, compared with the conventional MOSFET (semiconductordevice) in which a very thin inversion layer functions as the channel(current passage), on-resistance can be reduced largely.

In addition, the semiconductor device according to the third aspect, asdescribed above, the third region of an inverse conductivity type isfurther disposed in addition to the second region of one conductivitytype on the first region of one conductivity type, and the junctionportion between the first region of one conductivity type and the thirdregion of an inverse conductivity type makes a Zener diode. Thus, aZener diode can be connected between the source and the drain of theswitching transistor. Thus, even if static electricity, surge voltage orthe like enters the semiconductor device, the static electricity, thesurge voltage or the like can be absorbed by the Zener diode. Thus, itis possible to suppress dielectric breakdown or the like due to thestatic electricity, the surge voltage or the like entering thesemiconductor device. As a result, it is possible to suppress a breakageof the semiconductor device.

In addition, in the above-mentioned structure, the switching transistorand the Zener diode are integrated, so it is not necessary to disposeanother region or the like for forming a wiring member for connectingthe switching transistor with the Zener diode. Thus, an area of thecircuit including the switching transistor and the Zener diode that areconnected to each other can be reduced.

In the semiconductor device according to the third aspect, preferably,the electrode layer may further be formed on the upper surface of thesemiconductor layer, so that the second region and the third region areelectrically connected to each other via the electrode layer. With thisstructure, the Zener diode can easily be connected between the sourceand the drain of the switching transistor.

In the semiconductor device according to the third aspect, preferably,the semiconductor layer includes the first region of one conductivitytype, the second region of one conductivity type, the third region of aninverse conductivity type, and as well a Zener diode diffusion region ofone conductivity type disposed in the third region of an inverseconductivity type. The junction portion between the third region and theZener diode diffusion region makes a Zener diode. With this structure,the Zener diode can be connected between the source and the gate of theswitching transistor as well as between the source and the drain of theswitching transistor. Thus, it is possible to suppress dielectricbreakdown or the like of the semiconductor device due to staticelectricity, surge voltage or the like.

In this case, preferably, the Zener diode diffusion region iselectrically connected to a predetermined embedded electrode among theplurality of embedded electrodes. With this structure, the Zener diodecan easily be connected between the source and the gate of the switchingtransistor.

The semiconductor device according to the third aspect may have thestructure in which each region between the neighboring trenches isblocked with every depletion layer formed around each of the pluralityof trenches so that the current passage interrupted, while everydepletion layer formed around each of the plurality of trenches isdeleted so that the current passage is opened.

The semiconductor device according to the third aspect may have thestructure in which the plurality of embedded electrodes include twotypes that are first embedded electrodes and second embedded electrodesto which voltages are applied separately, and each region between theneighboring trenches is blocked with the depletion layer formed aroundevery trench among the plurality of trenches so that the current passageis interrupted, while the depletion layer formed around the trenchfilled with the first embedded electrode among the plurality of trenchesis deleted so that the current passage is opened.

In this case, second embedded electrode may have a Schottky contact withthe semiconductor layer inside the trench.

The semiconductor device according to the third aspect may furtherinclude a current passage interrupting diffusion region of an inverseconductivity type formed in each region between the neighboring trenchesof the semiconductor layer so as to be disposed with a predeterminedspace to the trench, in which each region between the neighboringtrenches is blocked with depletion layers formed around the trench andaround the current passage interrupting diffusion region so that thecurrent passage is interrupted, while the depletion layer formed aroundthe trench is deleted so that the current passage is opened.

Note that the semiconductor device according to the third aspect mayhave the structure in which when the current passage is interrupted, thedepletion layers formed around the neighboring trenches are connected toeach other. With this structure, the current passage (each regionbetween the neighboring trenches in the semiconductor layer) cansecurely be blocked with the depletion layer.

Further, in the semiconductor device according to the third aspect, adistance between the neighboring trenches may be set so that thedepletion layers formed around the neighboring trenches are overlappedwith each other. With this structure, the depletion layers formed aroundthe neighboring trenches can easily be connected to each other.

Effects of the Invention

As described above, according to the present invention, thesemiconductor device that can largely reduce on-resistance based on anew principle of operation can easily be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view illustrating a semiconductor deviceaccording to a first embodiment of the present invention.

FIG. 2 is a plan view illustrating a plane shape of a trench and adiffusion region of the semiconductor device according to the firstembodiment illustrated in FIG. 1.

FIG. 3 is an equivalent circuit diagram of the semiconductor deviceaccording to the first embodiment illustrated in FIG. 1.

FIG. 4 is a cross sectional view illustrating an operation of a regionfunctioning as a switching transistor of the semiconductor deviceaccording to the first embodiment of the present invention.

FIG. 5 is a cross sectional view illustrating an operation of the regionfunctioning as a switching transistor of the semiconductor deviceaccording to the first embodiment of the present invention.

FIG. 6 is a cross sectional view illustrating an operation of a regionfunctioning as a diode of the semiconductor device according to thefirst embodiment of the present invention.

FIG. 7 is a cross sectional view illustrating an operation of a regionfunctioning as the diode of the semiconductor device according to thefirst embodiment of the present invention.

FIG. 8 is a diagram illustrating an effect of the semiconductor deviceaccording to the first embodiment of the present invention.

FIG. 9 is a cross sectional view illustrating a structure of a regionfunctioning as a switching transistor of a semiconductor deviceaccording to a second embodiment of the present invention.

FIG. 10 is a cross sectional view illustrating an operation of theregion functioning as a switching transistor of the semiconductor deviceaccording to the second embodiment of the present invention.

FIG. 11 is a cross sectional view illustrating a structure of a regionfunctioning as a switching transistor of a semiconductor deviceaccording to a third embodiment of the present invention.

FIG. 12 is a cross sectional view illustrating an operation of theregion functioning as a switching transistor of the semiconductor deviceaccording to the third embodiment of the present invention.

FIG. 13 is a cross sectional view illustrating a structure of a regionfunctioning as a switching transistor of the semiconductor deviceaccording to a fourth embodiment of the present invention.

FIG. 14 is a cross sectional view illustrating an operation of a regionfunctioning as a switching transistor of a semiconductor deviceaccording to a fourth embodiment of the present invention.

FIG. 15 is a cross sectional view illustrating a semiconductor deviceaccording to a fifth embodiment of the present invention.

FIG. 16 is a plan view illustrating a plane shape of a trench and adiffusion region of the semiconductor device according to the fifthembodiment illustrated in FIG. 15.

FIG. 17 is a plan view illustrating the semiconductor device accordingto the fifth embodiment illustrated in FIG. 15 in a simplified manner.

FIG. 18 is an enlarged plan view of an A-part of FIG. 17.

FIG. 19 is an equivalent circuit diagram of the semiconductor deviceaccording to the fifth embodiment illustrated in FIG. 15.

FIG. 20 is a cross sectional view illustrating an operation of thesemiconductor device according to the fifth embodiment of the presentinvention.

FIG. 21 is a cross sectional view illustrating an operation of thesemiconductor device according to the fifth embodiment of the presentinvention.

FIG. 22 is a cross sectional view illustrating a structure of a regionfunctioning as a switching transistor of a semiconductor deviceaccording to a sixth embodiment of the present invention.

FIG. 23 is a cross sectional view illustrating an operation of theregion functioning as a switching transistor of the semiconductor deviceaccording to the sixth embodiment of the present invention.

FIG. 24 is a cross sectional view illustrating a structure of a regionfunctioning as a switching transistor of the semiconductor deviceaccording to a seventh embodiment of the present invention.

FIG. 25 is a cross sectional view illustrating an operation of a regionfunctioning as a switching transistor of the semiconductor deviceaccording to the seventh embodiment of the present invention.

FIG. 26 is a cross sectional view illustrating a structure of a regionfunctioning as a switching transistor of a semiconductor deviceaccording to an eighth embodiment of the present invention.

FIG. 27 is a cross sectional view illustrating an operation of theregion functioning as a switching transistor of the semiconductor deviceaccording to the eighth embodiment of the present invention.

FIG. 28 is a cross sectional view illustrating a semiconductor deviceaccording to a ninth embodiment of the present invention.

FIG. 29 is a plan view of the semiconductor device according to theninth embodiment illustrated in FIG. 28.

FIG. 30 is an enlarged view of a part of FIG. 29.

FIG. 31 is a cross sectional view illustrating connection positions ofembedded electrodes of the semiconductor device according to the ninthembodiment illustrated in FIG. 28.

FIG. 32 is an equivalent circuit diagram of the semiconductor deviceaccording to the ninth embodiment illustrated in FIG. 28.

FIG. 33 is a cross sectional view illustrating an operation of thesemiconductor device according to the ninth embodiment of the presentinvention.

FIG. 34 is a cross sectional view illustrating an operation of thesemiconductor device according to the ninth embodiment of the presentinvention.

FIG. 35 is a cross sectional view illustrating a semiconductor deviceaccording to a tenth embodiment of the present invention.

FIG. 36 is a plan view of a semiconductor device according to a tenthembodiment illustrated in FIG. 35.

FIG. 37 is an enlarged view of a part of FIG. 36.

FIG. 38 is an equivalent circuit diagram of the semiconductor deviceaccording to the tenth embodiment illustrated in FIG. 35.

FIG. 39 is a cross sectional view of a semiconductor device according toa variation example of the tenth embodiment of the present invention.

FIG. 40 is a cross sectional view illustrating a structure of a regionfunctioning as a switching transistor of a semiconductor deviceaccording to an eleventh embodiment of the present invention.

FIG. 41 is a cross sectional view illustrating an operation of theregion functioning as a switching transistor of the semiconductor deviceaccording to the eleventh embodiment of the present invention.

FIG. 42 is a cross sectional view illustrating a structure of a regionfunctioning as a switching transistor of a semiconductor deviceaccording to a twelfth embodiment of the present invention.

FIG. 43 is a cross sectional view illustrating an operation of theregion functioning as a switching transistor of the semiconductor deviceaccording to the twelfth embodiment of the present invention.

FIG. 44 is a cross sectional view illustrating a structure of a regionfunctioning as a switching transistor of a semiconductor deviceaccording to a thirteenth embodiment of the present invention.

FIG. 45 is a cross sectional view illustrating an operation of a regionfunctioning as a switching transistor of the semiconductor deviceaccording to the thirteenth embodiment of the present invention.

FIG. 46 is a cross sectional view illustrating a structure of aconventional MOSFET (semiconductor device).

EXPLANATION OF NUMERALS

1 N⁺ type silicon substrate (semiconductor layer)

2, 102, 202 N type epitaxial layer (semiconductor layer)

2 a region (inside region)

2 b region (outside region)

3, 3 a, 3 b, 3 c, 103, 103 a, 103 b, 103 c, 203, 203 a, 203 b, 203 ctrench

5, 105, 205 embedded electrode

5 a, 105 a, 205 a embedded electrode (first embedded electrode)

5 b, 105 b, 205 b embedded electrode (second embedded electrode)

7 P⁺ type diffusion region (diffusion region)

8 junction portion (Zener diode)

9, 41 upper surface electrode layer (electrode layer)

10 junction portion (Schottky barrier diode)

12, 32, 42, 52, 113, 132, 142, 152, 212, 242, 252, 262 current passage

14, 14 a, 14 b, 14 c, 14 d, 14 e, 114, 114 a, 114 b, 114 c, 114 d, 213,213 a, 213 b, 213 c, 213 d depletion layer

20, 30, 40, 50, 120, 130, 140, 150, 220, 230, 240, 250, 260semiconductor device

41 a, 141 a, 251 a embedded portion (second embedded electrode)

51, 151, 261 P⁺ type diffusion region (diffusion region for currentpassage interruption)

101, 201 N⁺ type silicon substrate (semiconductor layer, first region)

102 a, 202 a N type well region (second region)

102 b, 202 b P⁻ type region (third region)

102 c N type well region (fourth region)

107 N⁺ type diffusion region (diffusion region, first diffusion region)

107 a N⁺ type diffusion region (first part)

107 b N⁺ type diffusion region (second part)

107 c N⁺ type diffusion region (third part)

108 P⁺ type diffusion region (diffusion region, second diffusion region)

109, 141, 209, 251 source electrode (electrode layer)

207 a N⁺ type diffusion region (Zener diode diffusion region)

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment)

Hereinafter, with reference to FIGS. 1 to 3, a structure of asemiconductor device 20 according to a first embodiment will bedescribed.

The semiconductor device 20 according to the first embodiment includes aregion 20 a and a region 20 b disposed outside of the region 20 a asillustrated in FIGS. 1 and 2. Further, the region 20 a of thesemiconductor device 20 is adapted to function as normally-off typeswitching transistors, and the region 20 b of the semiconductor device20 is adapted to function as diodes (Zener diodes and Schottky barrierdiodes). In other words, the semiconductor device 20 of the firstembodiment has a structure in which the switching transistors and diodes(Zener diodes and Schottky barrier diodes) are disposed integrally.

As a concrete structure, in the semiconductor device 20 of the firstembodiment, an N type epitaxial layer 2 made of N type silicon having athickness of approximately 1 to 10 μm is formed on an upper surface ofan N⁺ type silicon substrate 1. An N type impurity is doped into the N⁺type silicon substrate 1 at high concentration so as to have a goodohmic contact with a back surface electrode layer 11 that will bedescribed later. In addition, an N type impurity is doped into the Ntype epitaxial layer 2 at a concentration (approximately 5×10¹⁵ to1×10¹⁸ cm⁻³) that is lower than the concentration in the N⁻ type siliconsubstrate 1. In addition, the N type epitaxial layer 2 includes a region2 a (corresponding to the region 20 a of the semiconductor device 20)and a region 2 b (corresponding to the region 20 b of the semiconductordevice 20) disposed outside of the region 2 a. Note that the N⁺ typesilicon substrate 1 and the N type epitaxial layer 2 is an example ofthe “semiconductor layer of one conductivity type” in the presentinvention. In addition, the regions 2 a and 2 b are examples of the“inside region” and the “outside region” in the present invention,respectively.

In addition, in the region 2 a of the N type epitaxial layer 2, thereare formed a plurality of trenches 3, which are dug in the thicknessdirection of the N type epitaxial layer 2. The plurality of trenches 3are formed by etching the N type epitaxial layer 2 from the uppersurface (principal surface) side. In other words, opening ends of theplurality of trenches 3 are positioned on the upper surface side of theN type epitaxial layer 2.

In addition, in a plan view, each of the plurality of trenches 3 isformed in an elongated shape extending in a predetermined direction (Ydirection) that is parallel to the upper surface of the N type epitaxiallayer 2. In addition, the plurality of trenches 3 are arranged in thedirection (X direction) that is parallel to the upper surface of the Ntype epitaxial layer 2 and is perpendicular to the extending directionof the trench 3 (Y direction) with spaces of approximately 0.05 to 0.3μm. Further, a depth of each of the plurality of trenches 3 is set toapproximately 0.5 to 12 μm. The depth of the trench 3 of the firstembodiment is set to be smaller than the thickness of the N typeepitaxial layer 2 (approximately 1 to 10 μm). Note that the trench 3 maypenetrate the N type epitaxial layer 2 so as to reach the N⁺ typesilicon substrate 1 (not shown). In addition, a width of each of theplurality of trenches 3 in the X direction is set to approximately 0.1to 1 μm. The above-mentioned trenches 3 are formed only in the region 2a of the N type epitaxial layer 2 and are not formed in the region 2 bof the N type epitaxial layer 2.

In addition, on the inner surface of each of the plurality of trenches3, there is formed a silicon oxide film (insulator film) 4 obtained by athermal oxidation process of the N type silicon constituting the N typeepitaxial layer 2, at a thickness of approximately 10 to 100 nm

In addition, on the inner surface of each of the plurality of trenches3, there is formed an embedded electrode 5 made of P type polysiliconvia the silicon oxide film 4. Each of the plurality of embeddedelectrodes 5 is filled in the corresponding trench 3 to a halfway depththereof. Note that a metal or the like can be used instead of the P typepolysilicon as a structural material of the embedded electrode 5.

In the structure of the first embodiment in which the plurality ofembedded electrodes 5 are disposed, by controlling the applied voltageto the plurality of embedded electrodes 5, it is possible to form adepletion layer around each of the plurality of trenches 3 or to deletethe formed depletion layer. Further, in the first embodiment, thedistance between the neighboring trenches 3 is set so that when thedepletion layer is formed around each of the plurality of trenches 3,the depletion layers formed around neighboring trenches 3 are overlappedwith each other. In other words, when the depletion layer is formedaround each of the plurality of trenches 3, the depletion layers formedaround neighboring trenches 3 are connected to each other. Therefore, inthe first embodiment, when the depletion layer is formed around each ofthe plurality of trenches 3, each region between the neighboringtrenches 3 in the N type epitaxial layer 2 can be blocked with thedepletion layers.

In addition, the plurality of embedded electrodes 5 of the firstembodiment are divided into two types of embedded electrodes 5 a and 5 bthat are applied with voltages separately. One type of embeddedelectrode 5 a is adapted to be applied with a voltage corresponding to apredetermined control signal (for switching between on and off). Inaddition, the other type of embedded electrode 5 b is electricallyconnected to an upper surface electrode layer 9 that will be describedlater. In other words, other type embedded electrodes 5 b is adapted tobe the same potential as the upper surface electrode layer 9. Inaddition, the embedded electrodes 5 a and 5 b are arranged alternatelyone by one in the X direction. Therefore, one embedded electrode 5 b (5a) is disposed between the two embedded electrode 5 a (5 b). Note thatthe embedded electrodes 5 a and 5 b are examples of the “first embeddedelectrode” and the “second embedded electrode” in the present invention,respectively.

In addition, an interlayer insulator film 6 made of a silicon oxide filmis embedded in the remaining part that is not filled with the embeddedelectrode 5 of each of the plurality of trenches 3 (part over theembedded electrode 5). Each of the plurality of interlayer insulatorfilms 6 is provided for insulating between the corresponding embeddedelectrode 5 and the upper surface electrode layer 9 that will bedescribed later. In addition, the thickness of each of the plurality ofinterlayer insulator films 6 is set to be the same as the depth of theremaining part that is not filled with the embedded electrode 5 of thecorresponding trench 3 (part over the embedded electrode 5). Therefore,the upper surface of each of the plurality of interlayer insulator films6 is flush with the upper surface of the N type epitaxial layer 2 (uppersurface of the upper end portion of each region between the neighboringtrenches 3).

In addition, on the upper surface portion of the region 2 a of the Ntype epitaxial layer 2 (upper end portion of each region between theneighboring trenches 3), there is formed a high concentration region 2 cin which the N type impurity is doped at high concentration by ioninjection so that a low concentration region is not exposed on the uppersurface side of the region 2 a of the N type epitaxial layer 2. Theconcentration of the high concentration region 2 c of the N typeepitaxial layer 2 is set so that a good ohmic contact can be obtainedwith the upper surface electrode layer 9 that will be described later,and is higher than concentration of the N type impurity in other part ofthe N type epitaxial layer 2. Further, the thickness of the highconcentration region 2 c of the N type epitaxial layer 2 (depth of theion injection) is set to be smaller than the thickness of the interlayerinsulator film 6. In other words, the lower end portion of the highconcentration region 2 c of the N type epitaxial layer 2 is positionedhigher than the upper end portion of the embedded electrode 5.

On the other hand, in the region 2 b of the N type epitaxial layer 2,there is formed a plurality of P⁺ type diffusion regions 7 in which Ptype impurity is doped at high concentration (approximately 1×10¹⁷ to1×10²⁰ cm⁻³). Each of the plurality of P⁺ type diffusion regions 7 isformed by ion injection of P type impurity from the upper surface sideof the N type epitaxial layer 2. In other words, the upper surface ofeach of the plurality of P⁺ type diffusion regions 7 is exposed on theupper surface side of the region 2 b of the N type epitaxial layer 2. Inaddition, concentration of each of the plurality of P⁺ type diffusionregions 7 is set so as to obtain a good ohmic contact with the uppersurface electrode layer 9 that will be described later. Note that the P⁺type diffusion region 7 is an example of the “diffusion region of aninverse conductivity type” in the present invention.

In addition, in a plan view, each of the plurality of P⁺ type diffusionregions 7 is formed in an elongated shape extending in the samedirection as the extending direction (Y direction) of the elongatedtrench 3. In addition, the plurality of P⁺ type diffusion regions 7 arearranged with predetermined spaces in the same direction as thearrangement direction (X direction) of the plurality of trenches 3.Further, the thickness of each of the plurality of P⁺ type diffusionregions 7 (depth of the ion injection) is set to approximately 0.5 to 10μm. In addition, the width of each of the plurality of P⁺ type diffusionregions 7 in the X direction is set to approximately 0.1 to 2 μm. Notethat the plurality of P⁺ type diffusion regions 7 are formed only in theregion 2 b of the N type epitaxial layer 2 and are not formed in theregion 2 a of the N type epitaxial layer 2.

In the structure of the first embodiment in which the plurality of P⁺type diffusion regions 7 are disposed, it is possible to make eachjunction portion 8 between each of the plurality of P⁺ type diffusionregions 7 and the N type epitaxial layer 2 function as a Zener diode. Inthe following description, the junction portion 8 is referred to as aZener diode 8. Note that in the first embodiment, breakdown voltage ofthe Zener diode 8 is set to be lower than withstand voltage of thesilicon oxide film 4.

Further, in the structure of the first embodiment in which the pluralityof P⁺ type diffusion regions 7 are disposed, the applied voltage to theplurality of P⁺ type diffusion regions 7 is controlled, so that thedepletion layer can be formed around each of the plurality of P⁺ typediffusion regions 7 or the formed depletion layer can be deleted. Then,in the first embodiment, the distance between the neighboring P⁺ typediffusion regions 7 is set so that the depletion layers formed aroundthe neighboring P⁺ type diffusion regions 7 are overlapped with eachother when the depletion layer is formed around each of the plurality ofP⁺ type diffusion regions 7. In other words, when the depletion layer isformed around each of the plurality of type diffusion regions 7, thedepletion layers formed around the neighboring P⁺ type diffusion regions7 are connected to each other. Therefore, in the first embodiment, whenthe depletion layer is formed around each of the plurality of P⁺ typediffusion regions 7, each region between the neighboring P⁺ typediffusion regions 7 in the N type epitaxial layer 2 is blocked with thedepletion layer.

In addition, on the upper surface of the N type epitaxial layer 2, thereis formed the upper surface electrode layer 9 constituted of a metallayer (e.g., aluminum layer) or the like. The upper surface electrodelayer 9 is formed so as to cover both the regions 2 a and 2 b of the Ntype epitaxial layer 2. Note that the upper surface electrode layer 9 isan example of the “electrode layer” in the present invention.

The upper surface electrode layer 9 covers opening ends of the pluralityof trenches 3 in the region 2 a of the N type epitaxial layer 2, and hasan ohmic contact with the upper end portion of each region between theneighboring trenches 3 (upper surface of the high concentration region 2a) of the N type epitaxial layer 2. In contrast, in the region 2 b ofthe N type epitaxial layer 2, the upper surface electrode layer 9 has anohmic contact with the exposed upper surface of each of the plurality ofP⁺ type diffusion regions 7.

Further, in the region 2 b of the N type epitaxial layer 2, the uppersurface electrode layer 9 has a Schottky contact with the upper endportion of each region between the neighboring P⁺ type diffusion regions7 in the N type epitaxial layer 2 (upper surface of the lowconcentration region). Therefore, each junction portion 10 between theupper surface electrode layer 9 and the upper end portion of each regionbetween the neighboring P⁺ type diffusion regions 7 in the N typeepitaxial layer 2 functions as a Schottky barrier diode. In thefollowing description, the junction portion 10 is referred to as aSchottky barrier diode 10.

Note that the upper surface electrode layer 9 functions as one of sourceand drain electrodes of the switching transistor (e.g., a sourceelectrode) in the region 20 a functioning as a switching transistor ofthe semiconductor device 20. In contrast, in the region 20 b functioningas a diode of the semiconductor device 20, the upper surface electrodelayer 9 functions as anode electrodes of the Zener diode 8 and theSchottky barrier diode 10.

In addition, on the back surface of the N⁺ type silicon substrate 1,there is formed a back surface electrode layer 11 having a multilayerstructure in which a plurality of metal layers are laminated. The backsurface electrode layer 11 has an ohmic contact with the back surface ofthe N⁺ type silicon substrate 1 over the entire region. Note that theback surface electrode layer 11 functions as the other electrode ofsource and drain electrodes of the switching transistor (e.g., a drainelectrode) in the region 20 a functioning as a switching transistor ofthe semiconductor device 20. In contrast, in the region 20 b functioningas a diode of the semiconductor device 20, the back surface electrodelayer 11 functions as cathode electrodes of the Zener diode 8 and theSchottky bather diode 10.

In the structure described above, in the region 20 a functioning as aswitching transistor of the semiconductor device 20, when a voltage isapplied between the upper surface electrode layer 9 and the back surfaceelectrode layer 11, current flowing between the upper surface electrodelayer 9 and the back surface electrode layer 11 (current flowing in thethickness direction of the N type epitaxial layer 2) passes through eachregion between the neighboring trenches 3 in the N type epitaxial layer2. In other words, each region between the neighboring trenches 3 in theN type epitaxial layer 2 functions as a current passage (channel) 12 ofthe switching transistor.

In addition, in the region 20 b functioning as a diode of thesemiconductor device 20, when a voltage is applied between the uppersurface electrode layer 9 and the back surface electrode layer 11 (whenthe applied voltage of the Zener diode 8 and the Schottky barrier diode10 is a forward bias), current that passes through the Schottky barrierdiode 10 flows in each region between the neighboring P⁺ type diffusionregions 7 in the N type epitaxial layer 2. In other words, each regionbetween the neighboring P⁺ type diffusion regions 7 in the N typeepitaxial layer 2 functions as a current passage 13 for the current thatpasses through the Schottky bather diode 10 to flow.

Further, the semiconductor device 20 of the first embodiment having theabove-mentioned structure can be represented by the equivalent circuitas illustrated in FIG. 3. In other words, as illustrated in FIG. 3, thesemiconductor device 20 of the first embodiment has the circuit in whichthe Zener diode and the Schottky barrier diode are electricallyconnected between the source and the drain of the switching transistor.Note that the part of the switching transistor of the semiconductordevice 20 is represented by a circuit symbol of a MOSFET in FIG. 3 forconvenience' sake.

Next, with reference to FIGS. 4 and 5, an operation of the region 20 afunctioning as a switching transistor of the semiconductor device 20according to the first embodiment will be described. Note that FIG. 4illustrates the case where the region 20 a functioning as a switchingtransistor of the semiconductor device 20 is in the turned-off statewhile FIG. 5 illustrates the case where the region 20 a functioning as aswitching transistor of the semiconductor device 20 is in the turned-onstate.

First, as illustrated in FIGS. 4 and 5, in the region 20 a functioningas a switching transistor, it is supposed that a negative potential anda positive potential are applied to the upper surface electrode layer(source electrode) 9 and the back surface electrode layer (drainelectrode) 11, respectively. Then, the negative potential is applied tothe embedded electrode 5 b because the embedded electrode 5 b iselectrically connected to the upper surface electrode layer (sourceelectrode) 9. Therefore, majority carrier is decreased around the trench3 filled with the embedded electrode 5 b (hereinafter referred to as atrench 3 b). In other words, a depletion layer 14 (14 b) is formedaround the trench 3 b regardless of the turned-on state or theturned-off state.

Further, as illustrated in FIG. 4, in the region 20 a functioning as aswitching transistor, if the semiconductor device 20 is in theturned-off state, the applied voltage to the embedded electrode 5 a iscontrolled so that majority carrier existing around the trench 3(hereinafter referred to as a trench 3 a) filled with the embeddedelectrode 5 a is decreased. Thus, a depletion layer 14 (14 a) is formedaround the trench 3 a similarly to the depletion layer 14 b formedaround the trench 3 b.

In this case, in the region 20 a functioning as a switching transistor,the depletion layers 14 a and 14 b formed around the trenches 3 a and 3b are overlapped with each other in the region between the trench 3 aand the trench 3 b. In other words, in the region between the trench 3 aand the trench 3 b, the depletion layers 14 a and 14 b are connected toeach other. Thus, current flowing through the current passage 12 can beinterrupted because the current passage 12 is blocked with the depletionlayers 14 a and 14 b. Therefore, the semiconductor device 20 is turnedoff.

Next, as illustrated in FIG. 5, in the region 20 a functioning as aswitching transistor, if the semiconductor device 20 is to be switchedfrom the turned-off state to the turned-on state, a predeterminedpositive potential is applied to the embedded electrode 5 a so that thedepletion layer 14 a formed around the trench 3 a (see FIG. 4) isdeleted. In other words, the depletion layer 14 a that blocks the partof the current passage 12 on the embedded electrode 5 a side is deleted.Thus, current can flow through the part of the current passage 12 on theembedded electrode 5 a side in the arrow direction in FIG. 5, so thatthe semiconductor device 20 can be turned on.

In addition, if the semiconductor device 20 is to be switched from theturned-on state to the turned-off state in the region 20 a functioningas a switching transistor, the application of the predetermined positivepotential to the embedded electrode 5 a is stopped. Thus, the stateillustrated in FIG. 4 is restored, so that the semiconductor device 20can be turned off.

Next, with reference to FIGS. 6 and 7, an operation of the region 20 bfunctioning as a diode of the semiconductor device 20 according to thefirst embodiment will be described. Note that FIG. 6 illustrates thestate where a reverse bias is applied to the region 20 b functioning asa diode of the semiconductor device 20 while FIG. 7 illustrates thestate where a forward bias is applied to the region 20 b functioning asa diode of the semiconductor device 20.

First, as illustrated in FIG. 6, in the region 20 b functioning as adiode, when the reverse bias is applied to between the upper surfaceelectrode layer (anode electrode) 9 and the back surface electrode layer(cathode electrode) 11, the negative potential is applied to the P⁺ typediffusion region 7 because the P⁺ type diffusion region 7 iselectrically connected the upper surface electrode layer (anodeelectrode) 9. Therefore, majority carrier is decreased around the P⁺type diffusion region 7. In other words, a depletion layer 14 (14 c) isformed around the P⁺ type diffusion region 7.

In this case, in the region 20 b functioning as a diode, the depletionlayers 14 c formed around the neighboring P⁺ type diffusion regions 7are overlapped with each other in the region between the neighboring P⁺type diffusion regions 7. In other words, in the region between theneighboring P⁺ type diffusion regions 7, the depletion layers 14 cformed around the neighboring P⁺ type diffusion regions 7 are connectedto each other. Thus, the current passage 13 is blocked with thedepletion layers 14 c, so that occurrence of leak current in theSchottky bather diode 10 is suppressed.

In addition, as illustrated in FIG. 7, in the region 20 b functioning asa diode, when a forward bias is applied between the upper surfaceelectrode layer (anode electrode) 9 and the back surface electrode layer(cathode electrode) 11, the positive potential is applied to the P⁺ typediffusion region 7 because the P⁺ type diffusion region 7 iselectrically connected to the upper surface electrode layer (anodeelectrode) 9. Therefore, the depletion layer 14 c (see FIG. 6) formedaround the P⁺ type diffusion region 7 is deleted. In other words, thedepletion layer 14 c that blocks the current passage 13 is deleted.Thus, the current that passes through the Schottky barrier diode 10flows through the current passage 13 in the arrow direction in FIG. 7.

In the first embodiment as described above, each region between theneighboring trenches 3 in the N type epitaxial layer 2 is blocked withthe depletion layer 14 formed around the trench 3 in the region 2 a ofthe N type epitaxial layer 2, so that the current passage 12 isinterrupted. In contrast, at least a part of the depletion layer 14formed around the trench 3 (depletion layer 14 a formed around thetrench 3 a) is deleted so that the current passage 12 is opened. Thus, aformation state of the depletion layer 14 formed around the trench 3changes in accordance with the applied voltage to the embedded electrode5. Therefore, by controlling the applied voltage to the embeddedelectrode 5, it is possible to switch from the turned-on state (in whichthe current passage 12 is opened) to the turned-off state (in which thecurrent passage 12 is interrupted), and to switch in the oppositedirection. In other words, the semiconductor device 20 can be used as aswitch device (switching transistor). Further, in the above-mentionedstructure, in the turned-on state, current can flow through the entirepart of the current passage 12 in which the depletion layer 14 isdeleted. Therefore, compared with the conventional MOSFET (semiconductordevice) in which a very thin inversion layer functions as the channel(current passage), resistance against current can be reduced largely.Thus, compared with the conventional MOSFET (semiconductor device) inwhich a very thin inversion layer functions as the channel (currentpassage), on-resistance can be reduced largely.

In addition, in the first embodiment, as described above, in the region2 b disposed on the outside of the region 2 a in the N type epitaxiallayer 2, the junction portion 8 between the N type epitaxial layer 2 andthe P⁺ type diffusion region 7 is adapted to be the Zener diode 8, sothat the Zener diode 8 is connected between the source and the drain ofthe switching transistor. Thus, even if noise voltage, surge voltage orthe like enters the semiconductor device 20, the noise voltage, thesurge voltage or the like can be absorbed by the Zener diode 8. Thus, itis possible to suppress malfunction such as breakage of thesemiconductor device 20 due to the noise voltage or the surge voltageentering the semiconductor device 20.

In addition, in the first embodiment, as described above, the junctionportion 10 between the each region between the neighboring P⁺ typediffusion regions 7 in the N type epitaxial layer 2 and the uppersurface electrode layer 9 constitutes the Schottky bather diode 10 inthe region 2 b of the N type epitaxial layer 2, so that the Zener diode8 and a Schottky bather diode 10 having a reverse recovery time shorterthan that of the Zener diode 8 are connected between the source and thedrain of the switching transistor. Thus, it is possible to suppress adecrease of switching speed.

In addition, according to the structure of the first embodimentdescribed above, the switching transistor, the Zener diode 8 and theSchottky barrier diode 10 are integrated. Therefore, it is not necessaryto dispose another region or the like for forming a wiring member forconnecting the switching transistor, the Zener diode 8 and the Schottkybarrier diode 10 to each other. Thus, an area of the circuit includingthe switching transistor, the Zener diode 8 and the Schottky barrierdiode 10 that are connected to each other can be reduced.

In addition, in the first embodiment, as described above, when a reversebias is applied to Schottky bather diode 10 in the region 2 b of the Ntype epitaxial layer 2, each region between the neighboring P⁺ typediffusion regions 7 in the N type epitaxial layer 2 is blocked with thedepletion layer 14 formed around the P⁺ type diffusion region 7. Thus,when the reverse bias is applied to the Schottky barrier diode 10,current flowing through each region between the neighboring P⁺ typediffusion regions 7 in the N type epitaxial layer 2 can be interrupted.Thus, occurrence of leak current in the Schottky barrier diode 10 can besuppressed. In this case, the depletion layers 14 formed around theneighboring P⁺ type diffusion regions 7 are connected to each other, sothat each region between the neighboring P⁺ type diffusion regions 7 inthe N type epitaxial layer 2 can securely be blocked with the depletionlayers 14.

In addition, in the first embodiment, as described above, the distancebetween the neighboring P⁺ type diffusion regions 7 is set so that thedepletion layers 14 formed around the neighboring P⁺ type diffusionregions 7 are overlapped with each other in the region 2 b of the N typeepitaxial layer 2. Thus, the depletion layers 14 formed around theneighboring P⁺ type diffusion regions 7 can easily be connected to eachother.

In addition, in the first embodiment, as described above, when thecurrent passage 12 is to be interrupted in the region 2 a of the N typeepitaxial layer 2, the depletion layers 14 formed around the neighboringtrenches 3 are connected to each other, so that the current passage 12can securely be blocked with the depletion layers 14.

In addition, in the first embodiment, as described above, the distancebetween the neighboring trenches 3 is set so that the depletion layers14 formed around the neighboring trenches 3 are overlapped with eachother in the region 2 a of the N type epitaxial layer 2. Thus, thedepletion layer 14 formed around the neighboring trenches 3 can easilybe connected to each other.

In addition, in the first embodiment, as described above, the interlayerinsulator film 6 is filled in the trench 3 so that the upper surface ofthe interlayer insulator film 6 becomes flush with the upper surface ofthe N type epitaxial layer 2 in the region 2 a of the N type epitaxiallayer 2. Thus, even if the distance between the neighboring trenches 3is made to be small, the part of the N type epitaxial layer 2 on theupper surface side (upper end portion of the region between theneighboring trenches 3) is not entirely covered with the interlayerinsulator film 6. Thus, the distance between the neighboring trenches 3can be reduced, so that the depletion layers 14 formed around theneighboring trenches 3 can easily be connected to each other.

In addition, as illustrated in FIG. 8, if a coil 21 or the like isconnected to the semiconductor device 20 of the first embodiment, energyfrom the coil 21 (illustrated by the arrow in FIG. 8) can be absorbed bythe Zener diode 8.

(Second Embodiment)

Hereinafter, with reference to FIG. 9, a structure of the region 30 afunctioning as a switching transistor of the semiconductor device 30according to the second embodiment will be described.

In the semiconductor device of the second embodiment 30, as illustratedin FIG. 9, there is disposed only the trench 3 (3 a) filled with theembedded electrode 5 (5 a) to which a predetermined control signal(signal for switching on and off) is applied in the region 30 afunctioning as a switching transistor.

Further, in the second embodiment, when a voltage is applied between theupper surface electrode layer 9 and the back surface electrode layer 11,current flows between the upper surface electrode layer 9 and the backsurface electrode layer 11 to as to pass through each region between theneighboring trenches 3 a. In other words, in the second embodiment, eachregion between the neighboring trenches 3 a functions as the currentpassage 32.

Note that other structure of the region 30 a functioning as a switchingtransistor of the semiconductor device 30 of the second embodiment isthe same as the structure of the region 20 a functioning as a switchingtransistor of the semiconductor device 20 of the first embodimentdescribed above. In addition, the structure of the region functioning asa diode of the semiconductor device 30 of the second embodiment (notshown) is the same as the structure of the region 20 b functioning as adiode of the semiconductor device 20 of the first embodiment.

Next, an operation of the region 30 a functioning as a switchingtransistor of the semiconductor device 30 of the second embodiment willbe described with reference to FIGS. 9 and 10.

First, in case of the turned-off state, as illustrated in FIG. 9, anegative potential is applied to every embedded electrode 5 a so thatthe depletion layer 14 (14 a) is formed around every trench 3 a. Thus,the current passage 32 is blocked with the depletion layer 14 a, so thatthe current flowing through the current passage 32 can be interrupted.

Further, in case of switching from the turned-off state to the turned-onstate, as illustrated in FIG. 10, a positive potential is applied toevery embedded electrode 5 a, so that every depletion layer 14 aillustrated in FIG. 9 is deleted. Thus, if the negative potential andthe positive potential are applied to the upper surface electrode layer9 and the back surface electrode layer 11, respectively, current canflow through the current passage 32 in the arrow direction in FIG. 10.

The effect of the second embodiment is the same as the effect of thefirst embodiment described above.

(Third Embodiment)

Hereinafter, with reference to FIG. 11, a structure of the region 40 afunctioning as a switching transistor of the semiconductor device 40according to the third embodiment will be described.

In the semiconductor device 40 of the third embodiment, as illustratedin FIG. 11, the region 40 a functioning as a switching transistorincludes a trench 3 (3 a) filled with an embedded electrode 5 (5 a) towhich a predetermined control signal is applied and a trench 3 (3 c)filled with a part of the upper surface electrode layer 41 (hereinafterreferred to as an embedded portion 41 a). The trenches 3 a and 3 c arearranged with predetermined spaces alternately one by one. In addition,the embedded portion 41 a of the upper surface electrode layer 41 has aSchottky contact with the epitaxial layer 2 inside the trench 3 c. Notethat the upper surface electrode layer 41 is an example of the“electrode layer” in the present invention, and the embedded portion 41a is an example of the “second embedded electrode” in the presentinvention.

Further, in the third embodiment, when a voltage is applied between theupper surface electrode layer 41 and the back surface electrode layer11, current flows between the upper surface electrode layer 41 and theback surface electrode layer 11 so as to pass through each regionbetween the trench 3 a and the trench 3 c. In other words, in the thirdembodiment, each region between the trench 3 a and the trench 3 cfunctions as the current passage 42.

Note that other structure of the region 40 a functioning as a switchingtransistor of the semiconductor device 40 of the third embodiment is thesame as the structure of the region 20 a functioning as a switchingtransistor of the semiconductor device 20 of the first embodimentdescribed above. In addition, the structure of the region functioning asa diode of the semiconductor device 40 of the third embodiment (notshown) is the same as the structure of the region 20 b functioning as adiode of the semiconductor device 20 of the first embodiment.

Next, with reference to FIGS. 11 and 12, an operation of the region 40 afunctioning as a switching transistor of the semiconductor device 40according to the third embodiment will be described.

Note that it is supposed that a negative potential and a positivepotential are applied to the upper surface electrode layer 41 and theback surface electrode layer 11, respectively, in the followingdescription of the operation. In other words, a depletion layer 14 (14d) is formed around the trench 3 c filled with the embedded portion 41 ain the upper surface electrode layer 41 regardless of the turned-onstate or the turned-off state.

First, in case of the turned-off state, as illustrated in FIG. 11, anegative potential is applied to the embedded electrode 5 a so that thedepletion layer 14 (14 a) is formed around the trench 3 a. Thus, thecurrent passage 42 is blocked with depletion layers 14 a and 14 d, sothat current flowing through the current passage 42 can be interrupted.

Further, in case of switching from the turned-off state to the turned-onstate, as illustrated in FIG. 12, a positive potential is applied to theembedded electrode 5 a so that the depletion layer 14 a illustrated inFIG. 11 is deleted. Thus, current can flow through the part of thecurrent passage 42 on the embedded electrode 5 a side in the arrowdirection in FIG. 12.

The effect of the third embodiment is the same as the effect of thefirst embodiment.

(Fourth Embodiment)

Hereinafter, with reference to FIG. 13, a structure of a region 50 afunctioning as a switching transistor of a semiconductor device 50according to a fourth embodiment will be described.

In the semiconductor device 50 of the fourth embodiment, as illustratedin FIG. 13, the region 50 a functioning as a switching transistorincludes the trench 3 (3 a) filled with the embedded electrode 5 (5 a)to which a predetermined control signal is applied as well as a P⁺ typediffusion region 51 into which P type impurity is doped at highconcentration. The P⁺ type diffusion region 51 is disposed in eachregion between the neighboring trenches 3 a with a predetermined apaceto the trench 3 a by one to one. In addition, the P⁺ type diffusionregion 51 has an ohmic contact with the upper surface electrode layer 9.Note that P⁺ type diffusion region 51 is an example of the “currentpassage interrupting diffusion region” in the present invention.

Further, in the fourth embodiment, when a voltage is applied between theupper surface electrode layer 9 and the back surface electrode layer 11,the current flowing between the upper surface electrode layer 9 and theback surface electrode layer 11 passes through each region between thetrench 3 a and the P⁺ type diffusion region 51. In other words, in thefourth embodiment, each region between the trench 3 a and the P⁺ typediffusion region 51 functions as a current passage 52.

Note that other structure of the region 50 a functioning as a switchingtransistor of the semiconductor device 50 of the fourth embodiment isthe same as the structure of the region 20 a functioning as a switchingtransistor of the semiconductor device 20 of the first embodiment. Inaddition, a structure of the region functioning as a diode of thesemiconductor device 50 of the fourth embodiment (not shown) is the sameas the structure of the region 20 b functioning as a diode of thesemiconductor device 20 of the first embodiment.

Next, with reference to FIGS. 13 and 14, an operation of the region 50 afunctioning as a switching transistor of the semiconductor device 50according to the fourth embodiment will be described.

Note that it is supposed that a negative potential and a positivepotential are applied to the upper surface electrode layer 9 and theback surface electrode layer 11, respectively, in the followingdescription of the operation. In other words, a depletion layer 14 (14e) is formed around the P⁺ type diffusion region 51, regardless of theturned-on state or the turned-off state.

First, in case of the turned-off state, as illustrated in FIG. 13, anegative potential is applied to the embedded electrode 5 a so that thedepletion layer 14 (14 a) is formed around the trench 3 a. Thus, thecurrent passage 52 is blocked with the depletion layers 14 a and 14 e,so that the current flowing through the current passage 52 can beinterrupted.

Further, in case of switching from the turned-off state to the turned-onstate, as illustrated in FIG. 14, a positive potential is applied to theembedded electrode 5 a, so that the depletion layer 14 a illustrated inFIG. 13 is deleted. Thus, the current can flow through the part of thecurrent passage 52 on the embedded electrode 5 a side in the arrowdirection in FIG. 14.

The effect of the fourth embodiment is the same as the effect of thefirst embodiment.

(Fifth Embodiment)

Hereinafter, with reference to FIGS. 15 to 19, a structure of asemiconductor device 120 according to a fifth embodiment of the presentinvention will be described.

As illustrated in FIGS. 15 to 17, the semiconductor device 120 accordingto the fifth embodiment includes a region 120 a and a region 120 b thatis disposed outside the region 120 a so as to enclose the region 120 ain a plan view. Further, the region 120 a of the semiconductor device120 is adapted to function as a normally-off type switching transistor.The region 120 b of the semiconductor device 120 is adapted to functionas a bidirectional Zener diode. In other words, the semiconductor device120 of the fifth embodiment has a structure in which the switchingtransistor and the bidirectional Zener diode are disposed integrally.

As a concrete structure, in the semiconductor device 120 of the fifthembodiment, an epitaxial layer 102 made of P⁻ type silicon having athickness of approximately 1 to 10 μm is formed on the upper surface ofthe N⁺ type silicon substrate 101. N type impurity is doped into the N⁺type silicon substrate 101 at high concentration so as to have a goodohmic contact with the drain electrode 110 that will be described later.Note that the N⁺ type silicon substrate 101 and the epitaxial layer 102are an example of the “semiconductor layer” in the present invention.

In addition, as illustrated in FIGS. 15 and 17, the epitaxial layer 102includes N type well regions 102 a and 102 c that are formed by dopingthe N type impurity, and a P⁻ type region 102 b that is a P⁻ typesilicon region constituting the epitaxial layer 102. In addition, the Ntype well regions 102 a and 102 c are formed respectively by doping Ntype impurity by ion injection from the upper surface side of theepitaxial layer 102 to a depth reaching the upper surface of the N⁺ typesilicon substrate 101. Note that N type impurity concentrations in the Ntype well regions 102 a and 102 c are, for example, approximately 5×10¹⁵to 1×10¹⁸ cm⁻³, while P type impurity concentration in the P⁻ typeregion 102 b is, for example, approximately 5×10¹⁵ to 1×10¹⁸ cm⁻³.

In addition, the N type well region 102 a is formed in the regioncorresponding to the region 120 a of the semiconductor device 120, whilethe P⁻ type region 102 b is formed in the region corresponding to theregion 120 b of the semiconductor device 120. In other words, the P⁻type region 102 b is formed in the region outside the N type well region102 a so as to enclose the N type well region 102 a in a plan view. Inaddition, the N type well region 102 c is formed in the region outsidethe P⁻ type region 102 b so as to enclose the P⁻ type region 102 b in aplan view. In other words, the N type well region 102 a, the P⁻ typeregion 102 b and the N type well region 102 c are formed in theepitaxial layer 102 so that the P⁻ type region 102 b is sandwichedbetween the N type well region 102 a and the N type well region 102 c.Note that the N⁺ type silicon substrate 101 is an example of the “firstregion of one conductivity type” in the present invention, and the Ntype well region 102 a is an example of the “second region of oneconductivity type” in the present invention. In addition, the P⁻ typeregion 102 b is an example of the “third region of an inverseconductivity type” in the present invention, and the N type well region102 c is an example of the “fourth region of one conductivity type” inthe present invention.

In addition, in the N type well region 102 a of the epitaxial layer 102,there are formed a plurality of trenches 103 that are dug in thethickness direction of the epitaxial layer 102. However, among theplurality of trenches 103, the trench 103 on each end side is formed ata boundary part between the N type well region 102 a and the P⁻ typeregion 102 b in the epitaxial layer 102. The plurality of trenches 103are formed by etching the epitaxial layer 102 from the upper surface(principal surface) side. In other words, opening ends of the pluralityof trenches 103 are disposed on the upper surface side of the epitaxiallayer 102.

In addition, as illustrated in FIG. 16, each of the plurality oftrenches 103 is formed in an elongated shape so as to extend in apredetermined direction (Y direction) parallel to the upper surface ofthe epitaxial layer 102 in a plan view. In addition, the plurality oftrenches 103 are arranged with spaces of approximately 0.05 to 0.3 μm inthe direction (X direction) that is parallel to the upper surface of theepitaxial layer 102 and is perpendicular to the extending direction ofthe trench 103 (Y direction). Further, the depth of each of theplurality of trenches 103 is set to approximately 0.5 to 5 μm so as tobe smaller than the thickness of the epitaxial layer 102 (approximately1 to 10 μm). In addition, the width of each of the plurality of trenches103 in the X direction is set to approximately 0.1 to 1 μm.

In addition, on the upper surface of each of the plurality of trenches103, there is formed a silicon oxide film 104 at a thickness ofapproximately 10 to 100 nm obtained by thermal oxidation process ofsilicon forming the epitaxial layer 102.

In addition, on the inner surface of each of the plurality of trenches103, there is formed an embedded electrode (gate electrode) 105 made ofP type polysilicon via the silicon oxide film 104. Each of the pluralityof embedded electrodes 105 is filled in the opposed trench 103 to ahalfway depth. Note that a metal or the like can be used instead of theP type polysilicon as a material of the embedded electrode 105.

In the structure of the fifth embodiment including the plurality ofembedded electrodes 105 as described above, the applied voltage to theplurality of embedded electrodes 105 is controlled so as to form adepletion layer around each of the plurality of trenches 103 or todelete the formed depletion layer. Further, in the fifth embodiment, adistance between the neighboring trenches 103 is set to a distance suchthat the depletion layers formed around the neighboring trenches 103 areconnected with each other when the depletion layer is formed around eachof the plurality of trenches 103. Therefore, in the fifth embodiment,when the depletion layer is formed around each of the plurality oftrenches 103, each region between the neighboring trenches 103 in theepitaxial layer 102 is blocked with the depletion layer.

In addition, the plurality of embedded electrodes 105 of the fifthembodiment include two types of embedded electrodes 105 a and 105 b towhich voltages are applied separately. One type embedded electrode 105 ais adapted to be applied with a voltage corresponding to a predeterminedcontrol signal (signal for switching on and off). In addition, othertype embedded electrodes 105 b is adapted to be electrically connected asource electrode 109 that will be described later. In other words, theother type embedded electrodes 105 b is adapted to be the same potentialas the source electrode 109. In addition, the embedded electrodes 105 aand 105 b are arranged alternately one by one in the X direction.Therefore, one embedded electrode 105 b (105 a) is disposed between twoembedded electrode 105 a (105 b). Note that the embedded electrodes 105a and 105 b are examples of the “first embedded electrode” and the“second embedded electrode” in the present invention.

In addition, an interlayer insulator film 106 made of a silicon oxidefilm is filled in the remaining part that is not filled with theembedded electrode 105 in each of the plurality of trenches 103 (partover the embedded electrode 105). Each of the plurality of interlayerinsulator films 106 is provided for insulating between the correspondingembedded electrode 105 and the source electrode 109 that will bedescribed later. In addition, the thickness of each of the plurality ofinterlayer insulator films 106 is set to be the same as the depth of theremaining part that is not filled with the embedded electrode 105 of thecorresponding trench 103 (part over the embedded electrode 105).Therefore, the upper surface of each of the plurality of interlayerinsulator films 106 is flush with the upper surface of the epitaxiallayer 102 (upper surface of the upper end portion of each region betweenthe neighboring trenches 103).

In addition, on the upper surface portion of the N type well region 102a in the epitaxial layer 102 (upper end portion of each region betweenthe neighboring trenches 103), there is formed a high concentrationregion 102 d in which N type impurity is doped at high concentration byion injection so that a low concentration region is not exposed on theupper surface side of the N type well region 102 a in the epitaxiallayer 102. The concentration of the high concentration region 102 d inthe epitaxial layer 102 is set so that a good ohmic contact can beobtained with the source electrode 109 that will be described later, andis higher than N type impurity concentration in other part of the N typewell region 102 a in the epitaxial layer 102. Further, the thickness ofthe high concentration region 102 d in the epitaxial layer 102 (depthafter diffusion by the ion injection) is set to be smaller than thethickness of the interlayer insulator film 106. In other words, thelower end portion of the high concentration region 102 d in theepitaxial layer 102 is positioned higher than the upper end portion ofthe embedded electrode 105.

On the other hand, as illustrated in FIG. 15, in the P⁻ type region 102b of the epitaxial layer 102, there are formed a plurality of N⁺ typediffusion regions 107 in which N type impurity is doped at highconcentration (e.g., approximately 1×10¹⁷ to 1×10²⁰ cm⁻³) and aplurality of P⁺ type diffusion regions 108 in which P type impurity isdoped at high concentration (e.g., approximately 1×10¹⁷ to 1×10²⁰ cm⁻³).Each of the plurality of N⁺ type diffusion regions 107 is formed by ioninjection of the N type impurity into the epitaxial layer 102 from theupper surface side thereof, and each of the plurality of P⁺ typediffusion regions 108 is formed by ion injection of the P type impurityinto the epitaxial layer 102 from the upper surface side thereof. Inaddition, the thickness of each of the plurality of P⁺ type diffusionregions 108 (depth after diffusion by the ion injection) is set to belarger than the thickness of the N⁺ type diffusion region 107 (depthafter diffusion by the ion injection). In other words, the lower endportion of the P⁺ type diffusion region 108 is positioned lower than thelower end portion of the N⁺ type diffusion region 107.

In addition, each of the N⁺ type diffusion regions 107 and each of theP⁺ type diffusion regions 108 are formed so as to enclose the N typewell region 102 a in a plan view as illustrated in FIGS. 17 and 18.Further, the N⁺ type diffusion regions 107 and the P⁺ type diffusionregions 108 are arranged alternately in a plan view. Specifically, asillustrated in FIGS. 15 and 18, one P⁺ type diffusion region 108 isdisposed between two N⁺ type diffusion regions 107 so as to contact withthe N⁺ type diffusion regions 107. Thus, the bidirectional Zener diodesconstituted of the plurality of N⁺ type diffusion regions 107 and theplurality of P⁺ type diffusion regions 108 are formed in the P⁻ typeregion 102 b of the epitaxial layer 102. Note that the plurality of N⁺type diffusion regions 107 and the plurality of P⁺ type diffusionregions 108 are examples of the “plurality of diffusion regions” in thepresent invention. In addition, the N⁺ type diffusion region 107 and theP⁺ type diffusion region 108 are examples of the “first diffusionregion” and the “second diffusion region”, respectively, in the presentinvention.

In addition, as illustrated in FIG. 15, on the upper surface of theepitaxial layer 102 (on the region corresponding to the region 120 a ofthe semiconductor device 120), there is formed a source electrode 109made of an aluminum layer or the like so as to cover the opening end ofeach of the plurality of trenches 103. The source electrode 109 has anohmic contact with the high concentration region 102 c in the epitaxiallayer 102 (upper end portion of each region between the neighboringtrenches 103) and also has an ohmic contact with the N⁺ type diffusionregion 107 a that is closest to the N type well region 102 a among theplurality of N⁺ type diffusion regions 107 constituting thebidirectional Zener diode. Note that the source electrode 109 is anexample of the “electrode layer” in the present invention, and the N⁺type diffusion region 107 a that is closest to the N type well region102 a is an example of the “first part” in the present invention.

In addition, on the lower surface (back surface) of the N⁺ type siliconsubstrate 101, there is formed a drain electrode 110 having a multilayerstructure in which a plurality of metal layers are laminated. The drainelectrode 110 has an ohmic contact with the lower surface (back surface)of the N⁺ type silicon substrate 101 over the entire region.

In addition, on the upper surface of the P⁻ type region 102 b in theepitaxial layer 102, there is formed an SiO₂ layer 111 so as to cover apredetermined region of the N⁺ type diffusion region 107 and the N⁺ typediffusion region 108. The SiO₂ layer 111 is formed so that a part of theupper surface of a predetermined N⁺ type diffusion region 107 c amongthe plurality of N⁺ type diffusion regions 107 constituting thebidirectional Zener diode is exposed. Note that the predetermined N⁺type diffusion region 107 c among the plurality of N⁺ type diffusionregions 107 is an example of the “third part” in the present invention.

Here, the N⁺ type diffusion region 107 b that is closest to the N typewell region 102 c among the plurality of N⁺ type diffusion regions 107constituting the bidirectional Zener diode is formed also in the N typewell region 102 c. Therefore, the N⁺ type diffusion region 107 b and theN⁺ type silicon substrate 101 (drain electrode 110) are electricallyconnected to each other via the N type well region 102 c. Thus, thebidirectional Zener diode is electrically connected between the sourceand the drain of the switching transistor in the semiconductor device120. Note that the N⁺ type diffusion region 107 b that is closest to theN type well region 102 c is an example of the “second part” in thepresent invention.

In addition, in a predetermined region on the upper surface of the P⁻type region 102 b in the epitaxial layer 102, there is formed a metallayer 112 that is electrically connected the embedded electrode 105 a. Apart of the metal layer 112 has an ohmic contact with a part of theupper surface of the exposed N⁺ type diffusion region 107 c. In otherwords, the metal layer 112 that is electrically connected to theembedded electrode 105 a is also electrically connected to thepredetermined N⁺ type diffusion region 107 c among the plurality of N⁺type diffusion regions 107 constituting the bidirectional Zener diode.Thus, the bidirectional Zener diode is electrically connected betweenthe source and the gate of the switching transistor in the semiconductordevice 120.

In the structure described above, when a voltage is applied between thesource electrode 109 and the drain electrode 110 in the region 120 afunctioning as a switching transistor in the semiconductor device 120,current flowing between the source electrode 109 and the drain electrode110 (current flowing in the thickness direction of the epitaxial layer102) passes through each region between the neighboring trenches 103 inthe epitaxial layer 102. In other words, each region between theneighboring trenches 103 in the epitaxial layer 102 functions as acurrent passage (channel) 113 of the switching transistor.

Further, the semiconductor device 120 of the fifth embodiment having theabove-mentioned structure can be represented by the equivalent circuitas illustrated in FIG. 19. In other words, as illustrated in FIG. 19,the semiconductor device 120 of the fifth embodiment has a circuit inwhich the bidirectional Zener diode is connected between the source andthe drain of the switching transistor as well as between the source andthe gate of the same. Note that the part of the switching transistor ofthe semiconductor device 120 is represented by a circuit symbol of aMOSFET for convenience' sake in FIG. 19.

Next, with reference to FIGS. 20 and 21, an operation of the region 120a functioning as a switching transistor in the semiconductor device 120of the fifth embodiment will be described. Note that FIG. 20 illustratesthe case where the semiconductor device that functions as a switchdevice is in the turned-off state, and FIG. 21 illustrates the casewhere the semiconductor device that functions as a switch device is inthe turned-on state.

First, as illustrated in FIGS. 20 and 21, it is supposed that a negativepotential and a positive potential are applied to the source electrode109 and the drain electrode 110, respectively. Then, the negativepotential is applied to the embedded electrode 105 b because theembedded electrode 105 b is electrically connected to the sourceelectrode 109. Therefore, majority carrier is decreased around thetrench 103 filled with the embedded electrode 105 b (hereinafterreferred to as a trench 103 b). In other words, a depletion layer 114(114 b) is formed the trench 103 b regardless of the turned-on state orthe turned-off state.

Further, as illustrated in FIG. 20, if the semiconductor device 120 isin the turned-off state, the applied voltage to the embedded electrode105 a is controlled so that majority carrier existing around the trench103 filled with the embedded electrode 105 a (hereinafter referred to asa trench 103 a) is decreased. Thus, the depletion layer 114 (114 a) isformed around the trench 103 a similarly to the depletion layer 114 (114b) formed around the trench 103 b.

In this case, the depletion layers 114 a and 114 b formed around thetrenches 103 a and 103 b are overlapped with each other in the regionbetween the trench 103 a and the trench 103 b. In other words, thedepletion layers 114 a and 114 b are connected to each other in theregion between the trench 103 a and the trench 103 b. Thus, the currentpassage 113 is blocked with the depletion layers 114 a and 114 b, sothat the current flowing through the current passage 113 can beinterrupted. Therefore, the semiconductor device 120 is turned off.

Next, as illustrated in FIG. 21, in case of switching the semiconductordevice 120 from the turned-off state to the turned-on state, apredetermined positive potential is applied to the embedded electrode105 a so that the depletion layer 114 a formed around the trench 103 a(see FIG. 20) is deleted. In other words, the depletion layer 114 ablocks the part on the embedded electrode 105 a side of the currentpassage 113 is deleted. Thus, current can flow through the part on theembedded electrode 105 a side of the current passage 113 in the arrowdirection in FIG. 21, so that the semiconductor device 120 can be turnedon.

In addition, in case of switching the semiconductor device 120 from theturned-on state to the turned-off state, the application of thepredetermined positive potential to the embedded electrode 105 a isstopped. Thus, the state illustrated in FIG. 20 is restored, so that thesemiconductor device 120 can be turned off.

In the fifth embodiment, as described above, each region between theneighboring trenches 103 in the epitaxial layer 102 is blocked with thedepletion layer 114 formed around the trench 103 in the N type wellregion 102 a of the epitaxial layer 102, so that the current passage 113is interrupted. In contrast, at least a part of the depletion layer 114formed around the trench 103 (depletion layer 114 a formed around thetrench 103 a) is deleted so that the current passage 113 is opened.Thus, a formation state of the depletion layer 114 formed around thetrench 103 changes in accordance with the applied voltage to theembedded electrode 105. Therefore, by controlling the applied voltage tothe embedded electrode 105, it is possible to switch from the turned-onstate (in which the current passage 113 is opened) to the turned-offstate (in which the current passage 113 is closed), and to switch in theopposite direction. In other words, the semiconductor device 120 can beused as a switch device (switching transistor). Further, in theabove-mentioned structure, in the turned-on state, the current can flowthrough the entire part of the current passage 113 in which thedepletion layer 114 is deleted. Therefore, compared with theconventional MOSFET (semiconductor device) in which a very thininversion layer functions as the channel (current passage), resistanceagainst current can be reduced largely. Thus, compared with theconventional MOSFET (semiconductor device) in which a very thininversion layer functions as the channel (current passage),on-resistance can be reduced largely.

In addition, in the fifth embodiment, as described above, thebidirectional Zener diodes in which the N⁺ type diffusions region 107and the P⁺ type diffusion regions 108 are arranged alternately areformed in the P⁻ type region 102 b of the epitaxial layer 102. Thus, thebidirectional Zener diode is connected between the source and the drainof the switching transistor in the semiconductor device 120 as well asbetween the source and the gate thereof. Thus, even if staticelectricity, surge voltage or the like enters the semiconductor device120, the bidirectional Zener diode can absorb the static electricity orthe surge voltage. Therefore, it is possible to suppress dielectricbreakdown or the like due to the input of the static electricity or thesurge voltage into the semiconductor device 120. As a result, it ispossible to suppress malfunction such as breakage of the semiconductordevice 120 due to the dielectric breakdown or the like.

In addition, in the structure of the fifth embodiment described above,by changing the number of the formed N⁺ type diffusion regions 107 andP⁺ type diffusion regions 108, Zener voltage (breakdown voltage) of thebidirectional Zener diode can easily be adjusted. Therefore, thebidirectional Zener diode having a predetermined Zener voltage(breakdown voltage) can easily be connected between the source and thedrain of the switching transistor as well as between the source and thegate of the same.

Further, in the structure of the fifth embodiment described above, theswitching transistor and the bidirectional Zener diode are integrated.Therefore, it is not necessary to dispose another region or the like forforming a wiring member for connecting the switching transistor and thebidirectional Zener diode. Thus, an area of the circuit including theswitching transistor and the bidirectional Zener diode that areconnected to each other can be reduced.

In addition, in the fifth embodiment, as described above, when thecurrent passage 113 is to be interrupted, the depletion layers 114formed around the neighboring trenches 103 are connected to each other.Thus, the current passage 113 can securely be blocked with the depletionlayers 114 formed around the neighboring trenches 103.

In addition, in the fifth embodiment, as described above, the interlayerinsulator film 106 is filled in each of the trenches 103 so that theupper surface of the interlayer insulator film 106 becomes flush withthe upper surface of the epitaxial layer 102. Thus, even if the distancebetween the neighboring trenches 103 is made to be small, the uppersurface side portion of the epitaxial layer 102 (upper end portion ofthe region between the neighboring trenches 103) is not coveredcompletely with the interlayer insulator film 106. Thus, the distancebetween the neighboring trenches 103 can be reduced, so that thedepletion layer 114 formed around the neighboring trenches 103 caneasily be connected to each other.

(Sixth Embodiment)

Hereinafter, with reference to FIG. 22, a structure of a region 130 afunctioning as a switching transistor of a semiconductor device 130according to a sixth embodiment will be described.

In the semiconductor device 130 of the sixth embodiment, the region 130a functioning as a switching transistor includes only the trench 103(103 a) filled with the embedded electrode 105 (105 a) to which apredetermined control signal (signal for switching on and off) isapplied.

Further, in the sixth embodiment, when a voltage is applied between thesource electrode 109 and the drain electrode 110, current flowingbetween the source electrode 109 and the drain electrode 110 passesthrough each region between neighboring trenches 103 a. In other words,in the sixth embodiment, each region between neighboring trenches 103 afunctions as a current passage 132.

Note that other structure of the region 130 a functioning as a switchingtransistor in the semiconductor device 130 of the sixth embodiment isthe same as the structure of the region 120 a functioning as a switchingtransistor in the semiconductor device 120 of the fifth embodiment. Inaddition, a structure of the region functioning as a bidirectional Zenerdiode in the semiconductor device 130 of the sixth embodiment (notshown) is the same as the structure of the region 120 b functioning as abidirectional Zener diode in the semiconductor device 120 of the fifthembodiment.

Next, with reference to FIGS. 22 and 23, an operation of the region 130a functioning as a switching transistor in the semiconductor device 130of the sixth embodiment will be described.

First, in case of the turned-off state, as illustrated in FIG. 22, anegative potential is applied to every embedded electrode 105 a so thatthe depletion layer 114 (114 a) is formed around every trench 103 a.Thus, the current passage 132 is blocked with the depletion layer 114 a,so that current flowing through the current passage 132 can beinterrupted.

Further, in case of switching from the turned-off state to the turned-onstate, as illustrated in FIG. 23, a positive potential is applied toevery embedded electrode 105 a, so that every depletion layer 114 aillustrated in FIG. 22 is deleted. Thus, if a negative potential and apositive potential are applied to the source electrode 109 and the drainelectrode 110, current can flow through the current passage 132 in thearrow direction illustrated in FIG. 23.

The effect of the sixth embodiment is the same as the effect of thefifth embodiment described above.

(Seventh Embodiment)

Hereinafter, with reference to FIG. 24, a structure of a region 140 afunctioning as a switching transistor of a semiconductor device 140according to a seventh embodiment will be described.

In the semiconductor device 140 of the seventh embodiment, the region140 a functioning as a switching transistor includes a trench 103 (103a) filled with an embedded electrode 105 (105 a) to which apredetermined control signal (signal for switching on and off) isapplied, and a trench 103 (103 c) filled with a part of a sourceelectrode 141 (hereinafter referred to as an embedded portion 141 a).The trenches 103 a and 103 c are arranged with predetermined spacesalternately one by one. In addition, the embedded portion 141 a of thesource electrode 141 has a Schottky contact with the epitaxial layer 102inside the trench 103 c. Note that the embedded portion 141 a of thesource electrode 141 is an example of the “second embedded electrode” inthe present invention.

Further, in the seventh embodiment, when a voltage is applied betweenthe source electrode 141 and the drain electrode 110, current flowsbetween the source electrode 141 and the drain electrode 110 so as topass through each region between the trench 103 a and the trench 103 c.In other words, in the seventh embodiment, each region between thetrench 103 a and the trench 103 c functions as a current passage 142.

Other structure of the region 140 a functioning as a switchingtransistor in the semiconductor device 140 of the seventh embodiment isthe same as the structure of the region 120 a functioning as a switchingtransistor in the above-mentioned semiconductor device 120 of the fifthembodiment. In addition, a structure of the region functioning as abidirectional Zener diode in the semiconductor device 140 of the seventhembodiment (not shown) is the same as the structure of the region 120 bfunctioning as a bidirectional Zener diode in the above-mentionedsemiconductor device 120 of the fifth embodiment.

Next, with reference to FIGS. 24 and 25, an operation of the region 140a functioning as a switching transistor in the semiconductor device 140of the seventh embodiment will be described.

Note that in the following description of the operation, it is supposedthat a negative potential and a positive potential are applied to eachof the source electrode 141 and the drain electrode 110. In other words,a depletion layer 114 (114 c) is formed around the trench 103 c filledwith the embedded portion 141 a of the source electrode 141, regardlessof the turned-on state or the turned-off state.

First, in case of the turned-off state, as illustrated in FIG. 24, anegative potential is applied to the embedded electrode 105 a so thatthe depletion layer 114 (114 a) is formed around the trench 103 a. Thus,the current passage 142 is blocked with the depletion layers 114 a and114 c, so that the current flowing through the current passage 142 canbe interrupted.

Further, in case of switching from the turned-off state to the turned-onstate, as illustrated in FIG. 25, a positive potential is applied to theembedded electrode 105 a, so that the depletion layer 114 a illustratedin FIG. 24 is deleted. Thus, current can flow through the part on theembedded electrode 105 a side (trench 103 a side) of the current passage142 in the arrow direction illustrated in FIG. 25.

The effect of the seventh embodiment is the same as the effect of thefifth embodiment.

(Eighth Embodiment)

Hereinafter, with reference to FIG. 26, a structure of a region 150 afunctioning as a switching transistor in a semiconductor device 150according to an eighth embodiment will be described.

In the semiconductor device 150 of the eighth embodiment, the region 150a functioning as a switching transistor includes a trench 103 (103 a)filled with the embedded electrode 105 (105 a) to which a predeterminedcontrol signal (signal for switching on and off) is applied, and a P⁺type diffusion region 151 in which P type impurity is doped at highconcentration. The P⁺ type diffusion region 151 is disposed in eachregion between the neighboring trenches 103 a with a predetermined spaceto the trench 103 a by one to one. In addition, the P⁺ type diffusionregion 151 has an ohmic contact with the source electrode 109. Note thatthe P⁺ type diffusion region 151 is an example of the “current passageinterrupting diffusion region” in the present invention.

Further, in the eighth embodiment, when a voltage is applied between thesource electrode 109 and the drain electrode 110, current flows betweenthe source electrode 109 and the drain electrode 110 so as to passthrough each region between the trench 103 a and the P⁺ type diffusionregion 151. In other words, in the eighth embodiment, each regionbetween the trench 103 a and the P⁺ type diffusion region 151 functionsas a current passage 152.

Note that other structure of the region 150 a functioning as a switchingtransistor in the semiconductor device 150 of the eighth embodiment isthe same as the structure of the region 120 a functioning as a switchingtransistor in the above-mentioned semiconductor device 120 of the fifthembodiment. In addition, a structure of the region functioning as abidirectional Zener diode in the semiconductor device 150 of the eighthembodiment (not shown) is the same as the structure of the region 120 bfunctioning as a bidirectional Zener diode in the above-mentionedsemiconductor device 120 of the fifth embodiment.

Next, with reference to FIGS. 26 and 27, an operation of the region 150a functioning as a switching transistor in the semiconductor device 150according to the eighth embodiment will be described.

Note that it is supposed that a negative potential and a positivepotential are applied to the source electrode 109 and the drainelectrode 110, respectively, in the following description of theoperation. In other words, a depletion layer 114 (114 d) is formedaround the P⁺ type diffusion region 151 regardless of the turned-onstate or the turned-off state.

First, in case of the turned-off state, as illustrated in FIG. 26, anegative potential is applied to the embedded electrode 105 a so thatthe depletion layer 114 (114 a) is formed around the trench 103 a. Thus,the current passage 152 is blocked with the depletion layers 114 a and114 d, so that current flowing through the current passage 152 can beinterrupted.

Further, in case of switching from the turned-off state to the turned-onstate, as illustrated in FIG. 27, a positive potential is applied to theembedded electrode 105 a, so that the depletion layer 114 a illustratedin FIG. 26 is deleted. Thus, current can flow through the part of thecurrent passage 152 on the embedded electrode 105 a side (trench 103 aside) in the arrow direction illustrated in FIG. 27.

The effect of the eighth embodiment is the same as the effect of thefifth embodiment described above.

(Ninth Embodiment)

Hereinafter, with reference to FIGS. 28 to 32, a structure of asemiconductor device 220 according to a ninth embodiment will bedescribed.

As illustrated in FIGS. 28 and 29, the semiconductor device 220 of theninth embodiment includes a region 220 a and a region 220 b disposedoutside the region 220 a. The regions 220 a and 220 b of thesemiconductor device 220 are arranged so that the region 220 b enclosesthe region 220 a in a plan view. Further, the region 220 a of thesemiconductor device 220 is adapted to function as a normally-off typeswitching transistor, while the region 220 b of the semiconductor device220 is adapted to function as a Zener diode. In other words, thesemiconductor device 220 of the ninth embodiment has a structure inwhich the switching transistor and the Zener diode are disposedintegrally.

As a concrete structure, in the semiconductor device 220 of the ninthembodiment, as illustrated in FIG. 28, an epitaxial layer 202 made of P⁻type silicon having a thickness of approximately 1 to 10 μm is formed onthe upper surface of the N⁺ type silicon substrate 201. N type impurityis doped in the N⁺ type silicon substrate 201 at high concentration soas to have a good ohmic contact with a drain electrode 210 that will bedescribed later. Note that the N⁺ type silicon substrate 201 is anexample of the “semiconductor layer” and the “first region of oneconductivity type” in the present invention, and the epitaxial layer 202is an example of the “semiconductor layer” in the present invention.

In addition, the epitaxial layer 202 includes N type well regions 202 aand 202 c, and a P⁻ type region 202 b. The N type well regions 202 a and202 c in the epitaxial layer 202 are formed by doping the N typeimpurity by ion injection from the upper surface side of the epitaxiallayer 202, and reach the upper surface of the N⁺ type silicon substrate201. In addition, the P⁻ type region 202 b in the epitaxial layer 202 isconstituted of the region in which the N type impurity is not doped byion injection. Note that the N type impurity concentration of the N typewell regions 202 a and 202 c in the epitaxial layer 202 is set toapproximately 5×10¹⁵ to 1×10¹⁸ cm⁻³, for example. In addition, the Ptype impurity concentration of the region in which the N type impurityis not doped by ion injection (P⁻ type region 202 b) in the epitaxiallayer 202 is set to approximately 5×10¹⁵ to 1×10¹⁸ cm⁻³, for example.

In addition, the N type well region 202 a of the epitaxial layer 202 isformed in every region corresponding to the region 220 a of thesemiconductor device 220, and the N type well region 202 c of theepitaxial layer 202 is formed at the outmost of the region correspondingto the region 220 b of the semiconductor device 220. Therefore, the P⁻type region 202 b of the epitaxial layer 202 is disposed inside the Ntype well region 202 c in the region corresponding to the region 220 bof the semiconductor device 220. Note that the N type well region 202 ais an example of the “second region of one conductivity type” in thepresent invention, and the P⁻ type region 202 b is an example of the“third region of an inverse conductivity type” in the present invention.

In addition, the N type well region 202 a of the epitaxial layer 202includes a plurality of trenches 203 dug in the thickness direction ofthe epitaxial layer 202. The plurality of trenches 203 are formed byetching the epitaxial layer 202 from the upper surface (principalsurface) side thereof. In other words, the opening end of each of theplurality of trenches 203 is disposed on the upper surface side of theepitaxial layer 202. Further, a depth of each of the plurality oftrenches 203 is set to approximately 0.5 to 12 μm. The depth of thetrench 203 in the ninth embodiment is set so as to be smaller than thethickness of the N type epitaxial layer 202 (approximately 1 to 10 μm).Note that the trench 203 may penetrate the N type epitaxial layer 202and reach the N⁻ type silicon substrate 201 (not shown).

In addition, as illustrated in FIGS. 29 and 30, each of the plurality oftrenches 203 is formed in an elongated shape so as to extend in apredetermined direction (Y direction) that is parallel to the uppersurface of the epitaxial layer 202 in a plan view. In addition, theplurality of trenches 203 are arranged with spaces of approximately 0.05to 0.3 μm in the direction (X direction) that is parallel to the uppersurface of the epitaxial layer 202 and is perpendicular to the extendingdirection of the trench 203 (Y direction). In addition, a width of eachof the plurality of trenches 203 in the X direction is set toapproximately 0.1 to 1 μm. Further, among the plurality of trenches 203,the trench 203 positioned at the endmost position is arranged tostraddle the boundary part between the N type well region 202 a and theP⁻ type region 202 b of the epitaxial layer 202.

In addition, as illustrated in FIG. 28, on the inner surface of each ofthe plurality of trenches 203, there is formed a silicon oxide film(insulator film) 204 that is obtained by thermal oxidation process ofsilicon forming the epitaxial layer 202 at a thickness of approximately10 to 100 nm.

In addition, on the inner surface of each of the plurality of trenches203, there is formed an embedded electrode 205 made of P typepolysilicon via the silicon oxide film 204. Each of the plurality ofembedded electrodes 205 is filled in the corresponding trench 203 to ahalfway depth. Note that a metal or the like can be used instead of theP type polysilicon as a material of the embedded electrode 205.

In the structure of the ninth embodiment in which the plurality ofembedded electrodes 205 are disposed as described above, the appliedvoltage to the plurality of embedded electrodes 205 is controlled so asto form the depletion layer around each of the plurality of trenches 203or to delete the formed depletion layer. Further, in the ninthembodiment, a distance between the neighboring trenches 203 is set sothat the depletion layers formed around the neighboring trenches 203 areoverlapped with each other when the depletion layer is formed aroundeach of the plurality of trenches 203. In other words, when thedepletion layer is formed around each of the plurality of trenches 203,the depletion layers formed around the neighboring trenches 203 areconnected to each other. Therefore, in the ninth embodiment, if thedepletion layer is formed around each of the plurality of trenches 203,each region between the neighboring trenches 203 can be blocked with thedepletion layers.

In addition, as illustrated in FIG. 31, the plurality of embeddedelectrodes 205 of the ninth embodiment include two types of embeddedelectrodes that are gate electrodes 205 a and common electrodes 205 b towhich voltages are applied separately. One type embedded electrodes(gate electrodes) 205 a are adapted to be applied with a voltagecorresponding to a predetermined control signal (signal for switching onand off). In addition, other type embedded electrodes (common electrode)205 b are electrically connected to a source electrode 209 that will bedescribed later. In other words, the other type embedded electrodes(common electrode) 205 b are adapted to be the same potential as thesource electrode 209. Note that the embedded electrodes 205 a and 205 bare example of the “first embedded electrode” and the “second embeddedelectrode” in the present invention, respectively.

In addition, as illustrated in FIG. 28, an interlayer insulator film 206made of a silicon oxide film is filled in the remaining part that is notfilled with the embedded electrode 205 in each of the plurality oftrenches 203 (part over the embedded electrode 205). Each of theplurality of interlayer insulator films 206 is provided for insulatingbetween the corresponding embedded electrode 205 and the sourceelectrode 209 that will be described later. In addition, the thicknessof each of the plurality of interlayer insulator films 206 is set to bethe same as the depth of the remaining part that is not filled with theembedded electrode 205 of the corresponding trench 203 (part over theembedded electrode 205). Therefore, the upper surface of each of theplurality of interlayer insulator films 206 is flush with the uppersurface of the epitaxial layer 202 (upper surface of the upper endportion of each region between the neighboring trenches 203).

In addition, on the upper surface portion of the N type well region 202a in the epitaxial layer 202 (upper end portion of each region betweenthe neighboring trenches 203), there is formed a high concentrationregion 202 d in which N type impurity is doped at high concentration byion injection so that a low concentration region is not exposed on theupper surface side of the epitaxial layer 202. The concentration of thehigh concentration region 202 d in the epitaxial layer 202 is set sothat a good ohmic contact can be obtained with the source electrode 209that will be described later, and is higher than the concentration inother part of the N type well region 202 a in the epitaxial layer 202.Further, the thickness of the high concentration region 202 d in theepitaxial layer 202 is set to be smaller than the thickness of theinterlayer insulator film 206. In other words, the lower end portion ofthe high concentration region 202 d in the epitaxial layer 202 ispositioned higher than the upper end portion of the embedded electrode205.

On the other hand, on at least a part of the P⁻ type region 202 b on theupper surface side in the epitaxial layer 202, there is formed a P⁺ typediffusion region 208 in which P type impurity is doped by ion injectionat high concentration (e.g., approximately 1×10¹⁷ to 1×10²⁰ cm⁻³) so asto have a good ohmic contact with the source electrode 209 that will bedescribed later. Further, on the upper surface side portion of the Ntype well region 202 c in the epitaxial layer 202, there is formed an N⁺type diffusion region 207 b in which N type impurity is doped by ioninjection at high concentration so that the N type well region 202 c isnot exposed on the upper surface of the epitaxial layer 202.

In addition, on the upper surface of the epitaxial layer 202, there isformed the source electrode 209 made of an aluminum layer or the like.The source electrode 209 has an ohmic contact with the highconcentration region 202 d of the epitaxial layer 202 (upper end portionof each region between the neighboring trenches 203) and the P⁺ typediffusion region 208. In other words, the N type well region 202 a andthe P⁻ type region 202 b of the epitaxial layer 202 are electricallyconnected to each other via the source electrode 209. Note that thesource electrode 209 is an example of the “electrode layer” in thepresent invention. In addition, on the back surface of the N⁺ typesilicon substrate 201, there is formed the drain electrode 210 made of amultilayer structure in which a plurality of metal layers are laminated.The drain electrode 210 has an ohmic contact with the N⁺ type siliconsubstrate 201.

In the structure described above, when a voltage is applied between thesource electrode 209 and the drain electrode 210, current flowingbetween the source electrode 209 and the drain electrode 210 (currentflowing in the thickness direction of the epitaxial layer 202) passesthrough at least a part of each region between the neighboring trenches203 in the epitaxial layer 202. In other words, at least a part of eachregion between the neighboring trenches 203 functions as a currentpassage (channel) 212 in the epitaxial layer 202.

Further, in the above-mentioned structure, a junction portion betweenthe P⁻ type region 202 b and the N⁺ type silicon substrate 201 functionsas a Zener diode in the epitaxial layer 202.

Note that the above-mentioned semiconductor device 220 of the ninthembodiment can be represented by an equivalent circuit illustrated inFIG. 32. In other words, as illustrated in FIG. 32, the semiconductordevice 220 of the ninth embodiment has a circuit in which a Zener diodeis connected between the source and the drain of a switching transistorso that the direction from the source to the drain of the switchingtransistor becomes a forward direction. Note that the part of theswitching transistor in the semiconductor device 220 is represented by acircuit symbol of a MOSFET in FIG. 32 for convenience' sake.

Next, with reference to FIGS. 33 and 34, an operation of the region 220a functioning as a switching transistor of the semiconductor device 220according to the ninth embodiment will be described. Note that FIG. 33illustrates the case where the region 220 a functioning as a switchingtransistor of the semiconductor device 220 is in the turned-off state,and FIG. 34 illustrates the case where the region 220 a functioning as aswitching transistor of the semiconductor device 220 is in the turned-onstate.

First, as illustrated in FIGS. 33 and 34, it is supposed that a negativepotential and a positive potential are applied to the source electrode209 and the drain electrode 210, respectively. Then, the embeddedelectrode (common electrode) 205 b is electrically connected to thesource electrode 209, so the negative potential is applied to theembedded electrode (common electrode) 205 b. Therefore, there is a statein which majority carrier is always decreased around the trench 203filled with the embedded electrode (common electrode) 205 b (hereinafterreferred to as a trench 203 b). In other words, a depletion layer 213(213 b) is always formed around the trench 203 b regardless of theturned-on state or the turned-off state.

Further, in case of the turned-off state, as illustrated in FIG. 33, theapplied voltage to the embedded electrode (gate electrode) 205 a iscontrolled so that majority carrier existing around the trench 203filled with the embedded electrode (gate electrode) 205 a (hereinafterreferred to as a trench 203 a) is decreased. Thus, a depletion layer 213(213 a) is formed around the trench 203 a similarly to the depletionlayer 213 b formed around the trench 203 b.

In this case, in the region between the trench 203 a and the trench 203b, the depletion layers 213 a and 213 b formed around the trench 203 aand the trench 203 b are overlapped with each other. In other words, inthe region between the trench 203 a and the trench 203 b, the depletionlayers 213 a and 213 b are connected to each other. Thus, the currentpassage 212 is blocked with the depletion layers 213 a and 213 b, sothat current flowing through the current passage 212 can be interrupted.

Further, in case of switching from the turned-off state to the turned-onstate, as illustrated in FIG. 34, a predetermined positive potential isapplied to the embedded electrode (gate electrode) 205 a, so that thedepletion layer 213 a formed around the trench 203 a (see FIG. 33) isdeleted. In other words, the depletion layer 213 a that blocks the partof the current passage 212 on the embedded electrode (gate electrode)205 a side is deleted. Thus, current can flow through the part of thecurrent passage 212 on the embedded electrode (gate electrode) 205 aside, so as to be turned on.

In addition, in case of switching from the turned-on state to theturned-off state, the application of the predetermined positivepotential to the embedded electrode (gate electrode) 205 a is stopped.Thus, the state illustrated in FIG. 33 is restored so as to be turnedoff.

In the ninth embodiment, as described above, each region between theneighboring trenches 203 is blocked with the depletion layer 213 formedaround the trench 203, so that the current passage 212 is interrupted.In contrast, at least a part of the depletion layer 213 formed aroundthe trench 203 (depletion layer 213 a formed around the trench 203 a) isdeleted so that the current passage 212 is opened. Thus, a formationstate of the depletion layer 213 changes in accordance with the appliedvoltage to the embedded electrode 205. Therefore, by controlling theapplied voltage to the embedded electrode 205, it is possible to switchfrom the turned-on state (in which the current passage 212 is opened) tothe turned-off state (in which the current passage 212 is interrupted),and to switch in the opposite direction. In other words, thesemiconductor device 220 can have a switching function. Further, in theabove-mentioned structure, in the turned-on state, the entire part ofthe current passage 212 in which the depletion layer 213 is deleted canbe used for the current to flow. Therefore, compared with theconventional semiconductor switch device (MOSFET) in which the very thininversion layer functions as a current passage (channel), resistanceagainst current can be reduced largely. Thus, compared with theconventional semiconductor switch device (MOSFET), on-resistance can bereduced largely.

In addition, in the ninth embodiment, as described above, the junctionportion between the N⁺ type silicon substrate 201 and the P⁻ type region202 b of the epitaxial layer 202 becomes the Zener diode, so that theZener diode is connected between the source and the drain of theswitching transistor. Thus, even if surge voltage or the like enters thesemiconductor device 220, the surge voltage or the like can be absorbedby the Zener diode. Therefore, it is possible to suppress dielectricbreakdown or the like due to the surge voltage entering thesemiconductor device 220. As a result, it is possible to suppress abreakage of the semiconductor device 220.

In addition, in the above-mentioned structure, the switching transistorand the Zener diode are integrated, so it is not necessary to disposeanother region or the like for forming a wiring member for connectingthe switching transistor with the Zener diode. Thus, an area of thecircuit including the switching transistor and the Zener diode that areconnected to each other can be reduced.

In addition, in the ninth embodiment, as described above, when thecurrent passage 212 is to be interrupted, the depletion layers 213formed around the neighboring trenches 203 are connected to each other,so that the current passage 212 can securely be blocked with thedepletion layers 213 formed around the neighboring trenches 203.

In addition, in the ninth embodiment, as described above, a distancebetween the neighboring trenches 203 is set so that the depletion layers213 formed around the neighboring trenches 203 are overlapped with eachother, so that the depletion layers 213 formed around the neighboringtrenches 203 can easily be connected to each other.

(Tenth Embodiment)

Hereinafter, with reference to FIGS. 35 to 38, a structure of asemiconductor device 230 according to a tenth embodiment will bedescribed.

The semiconductor device 230 of the tenth embodiment includes a region230 a and a region 230 b disposed so as to enclose the region 230 a asillustrated in FIGS. 35 to 37. The regions 230 a and 230 b in thesemiconductor device 230 are adapted to function as a switchingtransistor and a Zener diode, respectively.

Further, in the tenth embodiment, in the region corresponding to theregion 230 b of the semiconductor device 230, the P⁻ type region 202 bof the epitaxial layer 202 includes the P⁺ type diffusion region 208 andan N⁺ type diffusion region 207 a in which N type impurity is doped byion injection at high concentration (e.g., approximately 1×10¹⁷ to1×10²⁰ cm⁻³). Note that the N⁺ type diffusion region 207 a is an exampleof the “Zener diode diffusion region” in the present invention.

The N⁺ type diffusion region 207 a of the epitaxial layer 202 isdisposed at a predetermined part on the upper surface side of the P⁻type region 202 b so as not to contact with the P⁺ type diffusion region208. Further, the N⁺ type diffusion region 207 a in the epitaxial layer202 is electrically connected to the embedded electrode (gate electrode)205 a via a peripheral wiring 214. Note that the peripheral wiring 214is insulated by the SiO₂ layer 211 from a part other than the N⁺ typediffusion region 207 a in the epitaxial layer 202.

Note that other structure of the tenth embodiment is the same as theabove-mentioned ninth embodiment.

In the structure of the tenth embodiment, in addition to the junctionportion between the P⁻ type region 202 b in the epitaxial layer 202 andthe N⁺ type silicon substrate 201, a junction portion between the P⁻type region 202 b in the epitaxial layer 202 and the N⁺ type diffusionregion 207 a also functions as a Zener diode.

Further, the semiconductor device 230 of the tenth embodiment describedabove can be represented by an equivalent circuit as illustrated in FIG.38. In other words, in the semiconductor device 230 of the tenthembodiment, as illustrated in FIG. 38, a Zener diode is connectedbetween the source and the drain of the switching transistor so that thedirection from the source to the drain of the switching transistorbecomes the forward direction. In addition, another Zener diode isconnected between the source and the gate of the switching transistor sothat the direction from the source to the gate of the switchingtransistor becomes the forward direction. Note that the part of theswitching transistor in the semiconductor device 230 is represented by acircuit symbol of a MOSFET for convenience' sake in FIG. 38.

In the tenth embodiment, with the above-mentioned structure, it ispossible to connect the Zener diode also between the source and the gateof the switching transistor in addition to the Zener diode between thesource and the drain of the switching transistor. Thus, even if surgevoltage or the like enters the semiconductor device 230, the surgevoltage or the like can be absorbed by the two types of Zener diodes.Thus, dielectric breakdown or the like due to the surge voltage enteringthe semiconductor device 230 can be further suppressed. As a result, abreakage of the semiconductor device 230 can be further suppressed.

In addition, it is possible to adopt another structure illustrated inFIG. 39 as a variation example of the tenth embodiment, in which the P⁻type region 202 b is sandwiched between the N type well regions 202 a.

(Eleventh Embodiment)

Hereinafter, with reference to FIG. 40, a structure of a region 240 afunctioning as a switching transistor of a semiconductor device 240according to an eleventh embodiment will be described.

In the semiconductor device 240 of the eleventh embodiment, asillustrated in FIG. 40, there is formed only the trench 203 (203 a)filled with the embedded electrode 205 (205 a) to which a predeterminedcontrol signal (signal for switching on and off) is applied in theregion 240 a functioning as a switching transistor.

Further, in the eleventh embodiment, when a voltage is applied betweenthe source electrode 209 and the drain electrode 210, current flowingbetween the source electrode 209 and the drain electrode 210 passesthrough each region between the neighboring trenches 203 a. In otherwords, in the eleventh embodiment, each region between the neighboringtrenches 203 a functions as a current passage 242.

Note that other structure of the region 240 a functioning as a switchingtransistor of the semiconductor device 240 of the eleventh embodiment isthe same as the structure of the region 220 a functioning as a switchingtransistor of the semiconductor device 220 of the ninth embodimentdescribed above. In addition, a structure of the region functioning as aZener diode of the semiconductor device 240 of the eleventh embodiment(not shown) is the same as the structure of the region 220 b functioningas a Zener diode of the semiconductor device 220 of the ninth embodimentdescribed above or the region 230 b functioning as a Zener diode of thesemiconductor device 230 of the tenth embodiment described above.

Next, with reference to FIGS. 40 and 41, an operation of the region 240a functioning as a switching transistor of the semiconductor device 240of the eleventh embodiment will be described.

First, in case of the turned-off state, as illustrated in FIG. 40, anegative potential is applied to every embedded electrode 205 a so thatthe depletion layer 213 (213 a) is formed around every trench 203 a.Thus, the current passage 242 is blocked with the depletion layer 213 a,so that the current flowing through the current passage 242 can beinterrupted.

Further, in case of switching from the turned-off state to the turned-onstate, as illustrated in FIG. 41, a positive potential is applied toevery embedded electrode 205 a, so that every depletion layer 213 aillustrated in FIG. 40 is deleted. Thus, if a negative potential and apositive potential are applied to the source electrode 209 and the drainelectrode 210 respectively, current can flow through the current passage242 in the arrow direction illustrated in FIG. 41.

The effect of the eleventh embodiment is the same as the effect of theninth embodiment described above.

(Twelfth Embodiment)

Hereinafter, with reference to FIG. 42, a structure of a region 250 afunctioning as a switching transistor of a semiconductor device 250according to a twelfth embodiment will be described.

In the semiconductor device 250 of the twelfth embodiment, asillustrated in FIG. 42, the region 250 a functioning as a switchingtransistor includes a trench 203 (203 a) filled with the embeddedelectrode 205 (205 a) to which a predetermined control signal isapplied, and a trench 203 (203 c) filled with a part of the sourceelectrode 251 (hereinafter referred to as an embedded portion 251 a).The trenches 203 a and 203 c are arranged with predetermined spacesalternately one by one. In addition, the embedded portion 251 a of thesource electrode 251 has a Schottky contact with the epitaxial layer 202inside the trench 203 c. Note that the source electrode 251 is anexample of the “electrode layer” in the present invention, and theembedded portion 251 a is an example of the “second embedded electrode”in the present invention.

Further, in the twelfth embodiment, when a voltage is applied betweenthe source electrode 251 and the drain electrode 210, current flowsbetween the source electrode 251 and the drain electrode 210 so as topass through each region between the trench 203 a and the trench 203 c.In other words, in the twelfth embodiment, each region between thetrench 203 a and the trench 203 c functions as a current passage 252.

Note that other structure of the region 250 a functioning as a switchingtransistor in the semiconductor device 250 of the twelfth embodiment isthe same as the structure of the region 220 a functioning as a switchingtransistor in the semiconductor device 220 of the ninth embodimentdescribed above. In addition, a structure of the region functioning as adiode in the semiconductor device 250 of the twelfth embodiment (notshown) is the same as the structure of the region 220 b functioning as adiode in the semiconductor device 220 of the ninth embodiment describedabove or the region 230 b functioning as a Zener diode in thesemiconductor device 230 of the tenth embodiment described above.

Next, with reference to FIGS. 42 and 43, an operation of the region 250a functioning as a switching transistor in the semiconductor device 250according to the twelfth embodiment will be described.

Note that it is supposed in the following description of the operationthat a negative potential and a positive potential are applied to thesource electrode 251 and the drain electrode 210, respectively. In otherwords, a depletion layer 213 (213 c) is formed around the trench 203 cfilled with the embedded portion 251 a of the source electrode 251regardless of the turned-on state or the turned-off state.

First, in case of the turned-off state, as illustrated in FIG. 42, anegative potential is applied to the embedded electrode 205 a so thatthe depletion layer 213 (213 a) is formed around the trench 203 a. Thus,the current passage 252 is blocked with the depletion layers 213 a and213 c, so that the current flowing through the current passage 252 canbe interrupted.

Further, in case of switching from the turned-off state to the turned-onstate, as illustrated in FIG. 43, a positive potential is applied to theembedded electrode 205 a so that the depletion layer 213 a illustratedin FIG. 42 is deleted. Thus, current can flow through the part of thecurrent passage 252 on the embedded electrode 205 a side in the arrowdirection illustrated in FIG. 43.

The effect of the twelfth embodiment is the same as the effect of theninth embodiment as described above.

(Thirteenth Embodiment)

Hereinafter, with reference to FIG. 44, a structure of a region 260 afunctioning as a switching transistor of a semiconductor device 260according to a thirteenth embodiment will be described.

In the semiconductor device 260 of the thirteenth embodiment, asillustrated in FIG. 44, the region 260 a functioning as a switchingtransistor includes the trench 203 (203 a) filled with the embeddedelectrode 205 (205 a) to which the predetermined control signal isapplied, and also a P⁺ type diffusion region 261 in which P typeimpurity is doped at high concentration. The P⁺ type diffusion region261 is disposed in each region between the neighboring trenches 203 awith a predetermined space to the trench 203 a one to one. In addition,the P⁺ type diffusion region 261 has an ohmic contact with the sourceelectrode 209. Note that the P⁺ type diffusion region 261 is an exampleof the “current passage interrupting diffusion region” in the presentinvention.

Further, in the thirteenth embodiment, when a voltage is applied betweenthe source electrode 209 and the drain electrode 210, current flowsbetween the source electrode 209 and the drain electrode 210 so as topass through each region between the trench 203 a and the P⁺ typediffusion region 261. In other words, in the thirteenth embodiment, eachregion between the trench 203 a and the P⁺ type diffusion region 261functions as a current passage 262.

Note that other structure of the region 260 a functioning as a switchingtransistor in the semiconductor device 260 of the thirteenth embodimentis the same as the structure of the region 220 a functioning as aswitching transistor in the semiconductor device 220 of the ninthembodiment described above. In addition, a structure of the regionfunctioning as a Zener diode in the semiconductor device 260 of thetwelfth embodiment (not shown) is the same as the structure of theregion 220 b functioning as a Zener diode in the semiconductor device220 of the ninth embodiment or the region 230 b functioning as a Zenerdiode in the semiconductor device 230 of the tenth embodiment.

Next, with reference to FIGS. 44 and 45, an operation of the region 260a functioning as a switching transistor in the semiconductor device 260according to the thirteenth embodiment will be described.

Note that it is supposed that a negative potential and a positivepotential are applied to the source electrode 209 and the drainelectrode 210, respectively in the following description of theoperation. In other words, a depletion layer 213 (213 d) is formedaround the P⁺ type diffusion region 261 regardless of the turned-onstate or the turned-off state.

First, in case of the turned-off state, as illustrated in FIG. 44, anegative potential is applied to the embedded electrode 205 a so thatthe depletion layer 213 (213 a) is formed around the trench 203 a. Thus,the current passage 262 is blocked with the depletion layers 213 a and213 d, so that current flowing through the current passage 262 can beinterrupted.

Further, in case of switching from the turned-off state to the turned-onstate, as illustrated in FIG. 45, a positive potential is applied to theembedded electrode 205 a, so that the depletion layer 213 a illustratedin FIG. 44 is deleted. Thus, current can flow through the part of thecurrent passage 262 on the embedded electrode 205 a side in the arrowdirection in FIG. 45.

The effect of the thirteenth embodiment is the same as the effect of theninth embodiment.

Note that the embodiments disclosed here are merely examples in allpoints and should not be interpreted as a limitation. The scope of thepresent invention is defined not by the above description of theembodiments but by the claims, which includes every modification withinthe meaning and the range that are equivalent to the claims.

For instance, the first to the thirteenth embodiments have the structurein which the upper surface of the interlayer insulator film is flushwith the upper surface of the N type epitaxial layer, but the presentinvention is not limited to this structure. The upper surface of theinterlayer insulator film may be positioned higher than the uppersurface of the N type epitaxial layer, or the upper surface of theinterlayer insulator film may be positioned lower than the upper surfaceof the N type epitaxial layer.

In addition, the first to the thirteenth embodiments have the structurein which the depth of the trench is smaller than the thickness of theepitaxial layer, but the present invention is not limited to thisstructure. The trench may penetrate the epitaxial layer and reach the N⁺type silicon substrate. For instance, the depth of the trench may beapproximately 12 μm.

In addition, the first to the thirteenth embodiments exemplify thestructure using a silicon substrate as the substrate, but the presentinvention is not limited to this structure. A substrate made of SiC orthe like (semiconductor substrate) may be used.

In addition, the first to the fourth embodiments use the N typeepitaxial layer as the semiconductor layer of one conductivity type, butthe present invention is not limited to this structure. A P typeepitaxial layer may be used as the semiconductor layer of oneconductivity type.

In addition, the fifth to the thirteenth embodiment have the structurein which the plurality of trenches are formed in the N type well regionso that at least a part of each region between the neighboring trenchesin the N type well region functions as the current passage (channel),but the present invention is not limited to this structure. Theplurality of trenches may be formed in a P type well region so thatleast a part of each region between the neighboring trenches in the Ptype well region functions as the current passage (channel). In otherwords, it is possible to adopt a structure in which the conductivitytypes are reversed.

1. A semiconductor device comprising: a semiconductor layer of oneconductivity type including an inside region and an outside regiondisposed outside the inside region; a plurality of trenches formed inthe inside region of the semiconductor layer so as to be arranged withpredetermined spaces, an opening end of each of the trenches beingpositioned on an upper surface side of the semiconductor layer; aplurality of diffusion regions of an inverse conductivity type formed inthe outside region of the semiconductor layer so as to be arranged withpredetermined spaces, an upper surface of each of the diffusion regionsbeing exposed to the upper surface side of the semiconductor layer; aplurality of embedded electrodes filled in the plurality of trenches;and an electrode layer formed on the upper surface of the semiconductorlayer so as to cover the inside region and the outside region of thesemiconductor layer, wherein the semiconductor device switches betweenan on state and an off state according to a voltage applied to theplurality of embedded electrodes, in the inside region of thesemiconductor layer, a semiconductor region neighboring the plurality oftrenches is of the one conductivity type, in the inside region of thesemiconductor layer, an upper-surface-side part of each region betweenneighboring ones of the trenches of the semiconductor layer is ahigh-concentration region of the one conductivity type and is exposed tothe upper surface side of the semiconductor layer, in the inside regionof the semiconductor layer, in the off state, a depletion layer formedaround the trenches fills each region between neighboring ones of thetrenches of the semiconductor layer and, in the on state, at least partof the depletion layer disappears so that each region betweenneighboring ones of the trenches of the semiconductor layer serves as acurrent passage, and a junction portion between the semiconductor layerand the diffusion region makes a Zener diode in the outside region ofthe semiconductor layer.
 2. The semiconductor device according to claim1, wherein a junction portion between each region between theneighboring diffusion regions of the semiconductor layer and theelectrode layer makes a Schottky barrier diode in the outside region ofthe semiconductor layer.
 3. The semiconductor device according to claim2, wherein when a reverse bias is applied to the junction portionbetween each region between the neighboring diffusion regions of thesemiconductor layer and the electrode layer in the outside region ofthesemiconductor layer, each region between the neighboring diffusionregions of the semiconductor layer is blocked with a depletion layerformed around the diffusion region.
 4. The semiconductor deviceaccording to claim 3, wherein when a reverse bias is applied to thejunction portion between each region between the neighboring diffusionregions of the semiconductor layer and the electrode layer in theoutside region of the semiconductor layer, the depletion layers formedaround the neighboring diffusion region are connected to each other. 5.The semiconductor device according to claim 3, wherein a distancebetween the neighboring diffusion regions is set so that the depletionlayers formed around the neighboring diffusion regions are overlappedwith each other in the outside region of the semiconductor layer.
 6. Thesemiconductor device according to claim 1, wherein each region betweenthe neighboring trenches is blocked with every depletion layer formedaround each of the plurality of trenches so that the current passage isinterrupted, while every depletion layer formed around each of theplurality of trenches is deleted so that the current passage is opened.7. The semiconductor device according to claim 1, wherein the pluralityof embedded electrodes include two types that are first embeddedelectrodes and second embedded electrodes to which voltages are appliedseparately, and each region between the neighboring trenches is blockedwith the depletion layer formed around every trench among the pluralityof trenches so that the current passage is interrupted, while thedepletion layer formed around the trench filled with the first embeddedelectrode among the plurality of trenches is deleted so that the currentpassage is opened.
 8. The semiconductor devic 5 e according to claim 7,wherein the second embedded electrode has a Schottky contact with thesemiconductor layer inside the trench.
 9. The semiconductor deviceaccording to claim 1, further comprising a current passage interruptingdiffusion region of an inverse conductivity type formed in each regionbetween the neighboring trenches of the semiconductor layer so as to bedisposed with a predetermined space to the trench, wherein each regionbetween the neighboring trenches is blocked with depletion layers formedaround the trench and around the current passage interrupting diffusionregion so that the current passage is interrupted, while the depletionlayer formed around the trench is deleted so that the current passage isopened.
 10. A semiconductor device comprising: a semiconductor layerincluding first region of one conductivity type, and a second region ofone conductivity type as well as a third region of an inverseconductivity type formed on the first region; a plurality of trenchesformed in at least the second region of the semiconductor layer so as tobe arranged with predetermined spaces, an opening end of each of thetrenches being positioned on an upper surface side of the semiconductorlayer; and a plurality of embedded electrodes filled in the plurality oftrenches, wherein the semiconductor device switches between an on stateand an off state according to a voltage applied to the plurality ofembedded electrodes, in the second region of the semiconductor layer, asemiconductor region neighboring the plurality of trenches is of the oneconductivity type, in the second region of the semiconductor layer, anupper-surface-side part of each region between neighboring ones of thetrenches of the semiconductor layer is a high-concentration region ofthe one conductivity type and is exposed to the upper surface side ofthe semiconductor layer, in the second region of the semiconductorlayer, in the off state, a depletion layer formed around the trenchesfills each region between neighboring ones of the trenches of thesemiconductor layer and, in the on state, at least part of the depletionlayer disappears so that each region between neighboring ones of thetrenches of the semiconductor layer serves as a current passage, and abidirectional Zener diode constituted of the plurality of diffusionregions is formed in the third region of the semiconductor layer. 11.The semiconductor device according to claim 10, further comprising anelectrode layer formed on at least the second region of thesemiconductor layer, wherein the second region of the semiconductorlayer and a first part of the plurality of diffusion regionsconstituting the bidirectional Zener diode are electrically connectedvia the electrode layer.
 12. The semiconductor device according to claim11, further comprising a fourth region of one conductivity type formedon the first region, wherein a second part of the plurality of diffusionregions constituting the bidirectional Zener diode is electricallyconnected to the first region via the fourth region.
 13. Thesemiconductor device according to claim 11, wherein a third part of theplurality of diffusion regions constituting the bidirectional Zenerdiode is electrically connected a predetermined embedded electrode amongthe plurality of embedded electrodes.
 14. The semiconductor deviceaccording to claim 10, wherein the plurality of diffusion regionsconstituting the bidirectional Zener diode include first diffusionregions of one conductivity type and second diffusion regions of aninverse conductivity type, the first diffusion regions are arranged withpredetermined spaces, and the second diffusion region is arrangedbetween the neighboring first diffusion regions so as to contact withthe first diffusion regions in a plan view.
 15. The semiconductor deviceaccording to claim 12, wherein the third region is formed in a regionoutside the second region so as to enclose the second region in a planview, and the fourth region is formed in a region outside the thirdregion so as to enclose the third region in a plan view.
 16. Thesemiconductor device according to claim 10, wherein each region betweenthe neighboring trenches is blocked with every depletion layer formedaround each of the plurality of trenches so that the current passage isinterrupted, while every depletion layer formed around each of theplurality of trenches is deleted so that the current passage is opened.17. The semiconductor device according to claim 10, wherein theplurality of embedded electrodes include two types that are firstembedded electrodes and second embedded electrodes to which voltages areapplied separately, and each region between the neighboring trenches isblocked with the depletion layer formed around every trench among theplurality of trenches so that the current passage is interrupted, whilethe depletion layer formed around the trench filled with the firstembedded electrode among the plurality of trenches is deleted so thatthe current passage is opened.
 18. The semiconductor device according toclaim 17, wherein the second embedded electrode has a Schottky contactwith the semiconductor layer inside the trench.
 19. The semiconductordevice according to claim 10, further comprising a current passageinterrupting diffusion region of an inverse conductivity type formed ineach region between the neighboring trenches of the semiconductor layerso as to be disposed with a predetermined space to the trench, whereineach region between the neighboring trenches is blocked with depletionlayers formed around the trench and around the current passageinterrupting diffusion region so that the current passage isinterrupted, while the depletion layer formed around the trench isdeleted so that the current passage is opened.
 20. A semiconductordevice comprising: a semiconductor layer including first region of oneconductivity type, a second region of one conductivity type formed onthe first region and a third region of an inverse conductivity type; aplurality of trenches formed in at least the second region of thesemiconductor layer so as to be arranged with predetermined spaces; anda plurality of embedded electrodes filled in the plurality of trenches,wherein the semiconductor device switches between an on state and an offstate according to a voltage applied to the plurality of embeddedelectrodes, in the second region of the semiconductor layer, asemiconductor neighboring the plurality of trenches is of the oneconductivity type, in the second region of the semiconductor layer, anupper-surface-side part of each region between neighboring ones of thetrenches of the semiconductor layer is a high-concentration region ofthe one conductivity type and is exposed to the upper surface side ofthe semiconductor layer, in the second region of the semiconductorlayer, in the off state, a depletion layer formed around the trenchesfills each region between neighboring ones of the trenches of thesemiconductor layer and, in the on state, at least part of the depletionlayer disappears so that each region between neighboring ones of thetrenches of the semiconductor layer serves as a current passage, and ajunction portion between the first region and the third region makes aZener diode.
 21. The semiconductor device according to claim 20, furthercomprising an electrode layer formed on the upper surface of thesemiconductor layer, wherein the second region and the third region areelectrically connected to each other via the electrode layer.
 22. Thesemiconductor device according to claim 20, wherein the semiconductorlayer further includes a Zener diode diffusion region of oneconductivity type disposed in the third region of an inverseconductivity type in addition to the first region of one conductivitytype, the second region of one conductivity type and the third region ofan inverse conductivity type, and the junction portion between the thirdregion and the Zener diode diffusion region makes a Zener diode.
 23. Thesemiconductor device according to claim 22, wherein the Zener diodediffusion region is electrically connected to a predetermined embeddedelectrode among the plurality of embedded electrodes.
 24. Thesemiconductor device according to claim 20, wherein each region betweenthe neighboring trenches is blocked with every depletion layer formedaround each of the plurality of trenches so that the current passage isinterrupted, while every depletion layer formed around each of theplurality of trenches is deleted so that the current passage is opened.25. The semiconductor device according to claim 20, wherein theplurality of embedded electrodes include two types that are firstembedded electrodes and second embedded electrodes to which voltages areapplied separately, and each region between the neighboring trenches isblocked with the depletion layer formed around every trench among theplurality of trenches so that the current passage is interrupted, whilethe depletion layer formed around the trench filled with the firstembedded electrode among the plurality of trenches is deleted so thatthe current passage is opened.
 26. The semiconductor device according toclaim 25, wherein the second embedded electrode has a Schottky contactwith the semiconductor layer inside the trench.
 27. The semiconductordevice according to claim 20, further comprising a current passageinterrupting diffusion region of an inverse conductivity type formed ineach region between the neighboring trenches of the semiconductor layerso as to be disposed with a predetermined space to the trench, whereineach region between the neighboring trenches is blocked with depletionlayers formed around the trench and around the current passageinterrupting diffusion region so that the current passage isinterrupted, while the depletion layer formed around the trench isdeleted so that the current passage is opened.